feat(pocket-base): split hostile and passive mob spawning

README.md

@@ -29,7 +29,8 @@ The plugin JAR is written to `build/libs/`.
 /basesettings status
 /basesettings upgrade
 /basesettings pocket upgrade
-/basesettings pocket mobs <enable|disable>
+/basesettings pocket mobs <hostile|passive> <enable|disable>
+/basesettings pocket type <void|nether|overworld> <subtype>
 /basesettings visitors <allowed|blocked>
 /basesettings navigation <enable|disable>
 /basesettings flight <enable|disable>
@@ -44,7 +45,9 @@ After 250 Survival-mode block placements anywhere by default, the spawnable over
 
 `/base` has a stationary warm-up. Looking around is allowed, while movement between blocks, damage, teleportation, world changes, death, logout, and conflicting teleport commands cancel it without consuming the cooldown.
 
-Base IV owners can purchase and expand a persistent Pocket Base with `/basesettings pocket upgrade`. Activating a complete diamond-block portal frame inside the normal base with flint and steel opens one public entrance to the owner's grass platform in a private void world. Natural hostile and passive mob spawning is disabled by default and can be controlled by the owner with `/basesettings pocket mobs <enable|disable>`.
+Base IV owners can purchase and expand a persistent Pocket Base with `/basesettings pocket upgrade`. Activating a complete diamond-block portal frame inside the normal base with flint and steel opens one public entrance to the owner's grass platform in a private void world. The owner can move the return portal by building and igniting another complete frame inside the unlocked Pocket Base boundary; only the newly activated return portal remains functional. Natural hostile and passive mob spawning is disabled by default. Owners can control each category independently with `/basesettings pocket mobs <hostile|passive> <enable|disable>`.
+
+Owners can change biome metadata without altering Pocket Base blocks, entities, inventories, or portals by using `/basesettings pocket type <void|nether|overworld> <subtype>`. Void uses `the_void`; Nether and Overworld accept their compatible vanilla biome names, such as `crimson_forest` or `plains`. Each change defaults to 16 netherite blocks, is configurable, and affects applicable natural mob selection when spawning is enabled. The Pocket Base remains a void-generated normal-environment world; dimension-specific mechanics do not change.
 
 ## Administration
 

design/log.md

@@ -95,6 +95,22 @@ description: Chronological record of material decisions affecting the Spigot Bas
 ## 2026-08-24 — Pocket Base mob-spawning control
 
 - Disabled natural hostile and passive mob spawning by default in new and existing Pocket Bases without a saved preference.
-- Added the persisted owner setting `/basesettings pocket mobs enable|disable`, contextual autocomplete, and status reporting.
-- Reapplied saved spawn flags when Pocket Base worlds load and restored the prior world setting when persistence fails.
+- Added independent persisted owner settings through `/basesettings pocket mobs <hostile|passive> <enable|disable>`, contextual autocomplete, and status reporting.
+- Migrated each legacy combined mob-spawning preference to both categories to preserve existing behavior.
+- Reapplied both saved spawn flags when Pocket Base worlds load and restored both prior world settings when persistence fails.
+- Verified the feature with `./gradlew clean check jar`.
+
+## 2026-08-24 — Relocatable Pocket Base return portals
+
+- Allowed Pocket Base owners to activate a complete return portal frame with flint and steel anywhere inside their unlocked pocket boundary.
+- Persisted one active return portal location while retaining the generated portal as the default for existing Pocket Bases.
+- Made only the selected intact frame functional without removing old frame blocks, preserving the void-return safety fallback.
+- Verified the feature with `./gradlew clean check jar`.
+
+## 2026-08-24 — Purchasable Pocket Base biomes
+
+- Added `/basesettings pocket type <void|nether|overworld> <subtype>` with type-aware autocomplete and validation.
+- Defaulted new and unconfigured Pocket Bases to `void/the_void` and persisted each owner's selected biome.
+- Applied biome metadata across unlocked columns and new expansion rings without changing blocks, entities, inventories, portals, progression, or mob-spawning preferences.
+- Added an atomic, configurable biome-change payment that defaults to 16 netherite blocks and restores the prior biome and payment on failure.
 - Verified the feature with `./gradlew clean check jar`.

design/user-stories/index.md

@@ -24,3 +24,4 @@ description: Catalog of user stories for the Spigot Base plugin.
 16. [US-016: Build and use Pocket Base portals](us-016-build-and-use-pocket-base-portals.md)
 17. [US-017: Expand a Pocket Base](us-017-expand-a-pocket-base.md)
 18. [US-018: Control Pocket Base mob spawning](us-018-control-pocket-base-mob-spawning.md)
+19. [US-019: Change a Pocket Base biome](us-019-change-a-pocket-base-biome.md)

design/user-stories/us-016-build-and-use-pocket-base-portals.md

@@ -21,7 +21,12 @@ As a **Pocket Base owner**, I want to connect my normal base to my Pocket Base w
 - [x] Any player can use an active entrance without a separate visitor setting, warm-up, or cooldown.
 - [x] Visitors can build, break blocks, open containers, and otherwise interact normally inside the Pocket Base.
 - [x] The generated return portal sends players safely to the owner's active entrance.
-- [x] Return travel falls back to the server spawn when the owner has no valid active entrance.
+- [x] Only the owner can activate a complete portal frame inside their own Pocket Base with flint and steel.
+- [x] Every required return-frame block must be within the owner's unlocked Pocket Base boundary.
+- [x] Each Pocket Base has at most one active return portal, and activating another valid frame moves the active return location without removing the old frame.
+- [x] Relocated return portals persist through restarts, while existing Pocket Bases use the generated portal as their default.
+- [x] Breaking the active return frame disables return travel through it.
+- [x] Return travel falls back to the server spawn when the owner has no valid normal-world entrance.
 - [x] Falling below Y -64 performs the same safe return without void damage.
 - [x] Players who disconnect inside a Pocket Base remain there when they reconnect.
 - [x] Moving the normal base deactivates its entrance while preserving the Pocket Base world and its contents.

design/user-stories/us-018-control-pocket-base-mob-spawning.md

@@ -1,28 +1,31 @@
 ---
 type: User Story
 title: "US-018: Control Pocket Base mob spawning"
-description: Let Pocket Base owners control natural mob spawning in their private world, with spawning disabled by default.
+description: Let Pocket Base owners control hostile and passive natural mob spawning independently in their private world, with both disabled by default.
 status: done
 ---
 
 # US-018: Control Pocket Base mob spawning
 
-As a **Pocket Base owner**, I want to enable or disable natural mob spawning in my Pocket Base so that I can choose whether the private world supports normal mob activity.
+As a **Pocket Base owner**, I want to enable or disable hostile and passive natural mob spawning independently in my Pocket Base so that I can choose which kinds of normal mob activity its private world supports.
 
 ## Acceptance criteria
 
-- [x] Natural mob spawning is disabled by default in every new Pocket Base and in existing Pocket Bases that have no saved preference.
-- [x] A Pocket Base owner can use `/basesettings pocket mobs enable|disable` to control natural mob spawning in their own Pocket Base.
-- [x] The setting controls both hostile and passive natural spawning only in the owner's Pocket Base.
-- [x] The command is unavailable until Pocket Base I is unlocked.
-- [x] The command and its modes are offered through contextual autocomplete.
-- [x] `/basesettings status` displays the current Pocket Base mob-spawning setting.
-- [x] The preference persists across restarts and is reapplied when the Pocket Base world loads.
-- [x] Disabling natural spawning does not remove existing mobs or prevent explicitly spawned or summoned mobs.
-- [x] Persistence or world-application failures produce a clear failure message without reporting a successful change.
+- [x] Hostile and passive natural mob spawning are both disabled by default in every new Pocket Base and in existing Pocket Bases that have no saved preference.
+- [x] A Pocket Base owner can use `/basesettings pocket mobs hostile enable|disable` to control hostile natural mob spawning in their own Pocket Base.
+- [x] A Pocket Base owner can use `/basesettings pocket mobs passive enable|disable` to control passive natural mob spawning in their own Pocket Base.
+- [x] Changing one mob category does not change the other category.
+- [x] The commands are unavailable until Pocket Base I is unlocked.
+- [x] The commands, categories, and modes are offered through contextual autocomplete.
+- [x] `/basesettings status` displays the current hostile and passive Pocket Base mob-spawning settings.
+- [x] Both preferences persist across restarts and are reapplied when the Pocket Base world loads.
+- [x] Existing saved `mob-spawning-enabled` values migrate to both category preferences, preserving prior behavior.
+- [x] Disabling either natural-spawning category does not remove existing mobs or prevent explicitly spawned or summoned mobs.
+- [x] Persistence or world-application failures produce a clear failure message, restore both prior world flags, and do not report a successful change.
 
 ## Related
 
 - [US-015: Unlock a Pocket Base](us-015-unlock-a-pocket-base.md)
 - [US-016: Build and use Pocket Base portals](us-016-build-and-use-pocket-base-portals.md)
 - [US-017: Expand a Pocket Base](us-017-expand-a-pocket-base.md)
+- [US-019: Change a Pocket Base biome](us-019-change-a-pocket-base-biome.md)

design/user-stories/us-019-change-a-pocket-base-biome.md

@@ -0,0 +1,31 @@
+---
+type: User Story
+title: "US-019: Change a Pocket Base biome"
+description: Let Pocket Base owners purchase biome changes that alter natural mob selection without changing their builds.
+status: done
+---
+
+# US-019: Change a Pocket Base biome
+
+As a **Pocket Base owner**, I want to change my Pocket Base biome so that I can control its biome-specific atmosphere and natural mob selection without rebuilding it.
+
+## Acceptance criteria
+
+- [x] A Pocket Base owner can use `/basesettings pocket type <void|nether|overworld> <subtype>` to select a compatible biome.
+- [x] Void supports `the_void`; Nether supports its vanilla biome subtypes; and Overworld supports its vanilla biome subtypes.
+- [x] New and previously unconfigured Pocket Bases default to the void type and `the_void` subtype.
+- [x] Each change atomically charges a configurable currency and amount that default to 16 netherite blocks.
+- [x] Selecting the active subtype or providing an invalid type/subtype combination is rejected without charging.
+- [x] Changing subtypes within the same type incurs the configured cost.
+- [x] The selected biome is applied across every unlocked Pocket Base column without changing blocks, entities, inventories, portals, level, or the mob-spawning preference.
+- [x] Newly unlocked terrain receives the selected biome.
+- [x] When natural mob spawning is enabled, Minecraft can use the selected biome for applicable natural mob selection.
+- [x] The selected type and subtype persist through restarts and appear in `/basesettings status`.
+- [x] The command, types, and compatible subtypes are offered through contextual autocomplete.
+- [x] Failed biome application or persistence restores the prior biome and does not consume payment.
+
+## Related
+
+- [US-015: Unlock a Pocket Base](us-015-unlock-a-pocket-base.md)
+- [US-017: Expand a Pocket Base](us-017-expand-a-pocket-base.md)
+- [US-018: Control Pocket Base mob spawning](us-018-control-pocket-base-mob-spawning.md)

src/main/java/games/dmg/spigotbase/BaseSettingsCommand.java

@@ -20,6 +20,9 @@ final class BaseSettingsCommand implements CommandExecutor, TabCompleter {
     );
     private static final List<String> VISITOR_MODES = List.of("allowed", "blocked");
     private static final List<String> ENABLE_MODES = List.of("enable", "disable");
+    private static final List<String> POCKET_WORLD_TYPES = List.of(
+        "void", "nether", "overworld"
+    );
     private final BaseStateManager stateManager;
     private final PluginSettingsProvider settings;
     private final TeleportPolicy teleportPolicy;
@@ -66,9 +69,13 @@ final class BaseSettingsCommand implements CommandExecutor, TabCompleter {
                 && arguments[1].equalsIgnoreCase("upgrade")) {
             return purchasePocketUpgrade(player, state);
         }
-        if (arguments.length == 3 && arguments[0].equalsIgnoreCase("pocket")
+        if (arguments.length == 4 && arguments[0].equalsIgnoreCase("pocket")
                 && arguments[1].equalsIgnoreCase("mobs")) {
-            return updatePocketMobSpawning(player, arguments[2]);
+            return updatePocketMobSpawning(player, arguments[2], arguments[3]);
+        }
+        if (arguments.length == 4 && arguments[0].equalsIgnoreCase("pocket")
+                && arguments[1].equalsIgnoreCase("type")) {
+            return purchasePocketBiome(player, arguments[2], arguments[3]);
         }
         if (arguments.length == 2 && arguments[0].equalsIgnoreCase("visitors")) {
             return updateVisitors(player, state, arguments[1]);
@@ -180,7 +187,64 @@ final class BaseSettingsCommand implements CommandExecutor, TabCompleter {
         return true;
     }
 
-    private boolean updatePocketMobSpawning(Player player, String mode) {
+    private boolean purchasePocketBiome(
+        Player player,
+        String worldTypeName,
+        String biomeName
+    ) {
+        if (pocketBases == null) {
+            player.sendMessage(ChatColor.RED + "Pocket Bases are currently unavailable.");
+            return true;
+        }
+        PocketBaseState current = pocketBases.state(player.getUniqueId());
+        if (current.level() < 1) {
+            player.sendMessage(ChatColor.RED + "Pocket Base I is still locked.");
+            return true;
+        }
+        PocketBaseBiome biome = PocketBaseWorldType.fromCommand(worldTypeName)
+            .flatMap(worldType -> PocketBaseBiome.fromCommand(worldType, biomeName))
+            .orElse(null);
+        if (biome == null) {
+            player.sendMessage(ChatColor.RED + "That Pocket Base type and subtype are invalid.");
+            return true;
+        }
+        if (biome == current.biome()) {
+            player.sendMessage(ChatColor.RED + "Your Pocket Base already uses "
+                + biome.commandName() + ".");
+            return true;
+        }
+        int price = settings.current().pocketBaseBiomeChangeCost();
+        Material currency = Material.valueOf(
+            settings.current().pocketBaseBiomeCurrencyMaterial()
+        );
+        PlayerInventory inventory = player.getInventory();
+        if (countCurrency(inventory, currency) < price) {
+            player.sendMessage(ChatColor.RED + "Changing Pocket Base biome costs "
+                + price + " " + currency.name().toLowerCase(Locale.ROOT) + ".");
+            return true;
+        }
+        ItemStack[] snapshot = cloneContents(inventory.getStorageContents());
+        removeCurrency(inventory, currency, price);
+        final PocketBaseState updated;
+        try {
+            updated = pocketBases.setBiome(player.getUniqueId(), biome);
+        } catch (IOException | RuntimeException exception) {
+            inventory.setStorageContents(snapshot);
+            player.sendMessage(ChatColor.RED
+                + "The Pocket Base biome change failed; your payment was restored.");
+            return true;
+        }
+        player.sendMessage(ChatColor.GREEN + "Pocket Base biome changed to "
+            + updated.biome().commandName() + " for " + price + " "
+            + currency.name().toLowerCase(Locale.ROOT) + ".");
+        return true;
+    }
+
+    private boolean updatePocketMobSpawning(
+        Player player,
+        String category,
+        String mode
+    ) {
         if (pocketBases == null) {
             player.sendMessage(ChatColor.RED + "Pocket Bases are currently unavailable.");
             return true;
@@ -196,17 +260,30 @@ final class BaseSettingsCommand implements CommandExecutor, TabCompleter {
             return true;
         }
         final PocketBaseState updated;
+        final boolean settingEnabled;
         try {
-            updated = pocketBases.setMobSpawning(player.getUniqueId(), enabled);
+            if (category.equalsIgnoreCase("hostile")) {
+                updated = pocketBases.setHostileMobSpawning(
+                    player.getUniqueId(), enabled
+                );
+                settingEnabled = updated.hostileMobSpawningEnabled();
+            } else if (category.equalsIgnoreCase("passive")) {
+                updated = pocketBases.setPassiveMobSpawning(
+                    player.getUniqueId(), enabled
+                );
+                settingEnabled = updated.passiveMobSpawningEnabled();
+            } else {
+                sendUsage(player);
+                return true;
+            }
         } catch (IOException | RuntimeException exception) {
             player.sendMessage(ChatColor.RED
                 + "The Pocket Base mob-spawning setting could not be changed.");
             return true;
         }
-        player.sendMessage(ChatColor.YELLOW + "Pocket Base mob spawning is now "
-            + (updated.mobSpawningEnabled()
-                ? ChatColor.GREEN + "enabled"
-                : ChatColor.RED + "disabled")
+        player.sendMessage(ChatColor.YELLOW + "Pocket Base "
+            + category.toLowerCase(Locale.ROOT) + " mob spawning is now "
+            + (settingEnabled ? ChatColor.GREEN + "enabled" : ChatColor.RED + "disabled")
             + ChatColor.YELLOW + ".");
         return true;
     }
@@ -452,8 +529,12 @@ final class BaseSettingsCommand implements CommandExecutor, TabCompleter {
         player.sendMessage(colorForPrerequisite(owner.baseLevel() >= 4 && owner.base().isPresent())
             + "Pocket Base " + pocket.level() + ": " + ChatColor.GRAY + price + " "
             + settings.current().pocketBaseCurrencyMaterial().toLowerCase(Locale.ROOT)
-            + " → /basesettings pocket upgrade; mob spawning="
-            + (pocket.mobSpawningEnabled() ? "enabled" : "disabled"));
+            + " → /basesettings pocket upgrade; type="
+            + pocket.biome().worldType().commandName() + "/" + pocket.biome().commandName()
+            + "; hostile spawning="
+            + (pocket.hostileMobSpawningEnabled() ? "enabled" : "disabled")
+            + "; passive spawning="
+            + (pocket.passiveMobSpawningEnabled() ? "enabled" : "disabled"));
     }
 
     private void showCooldownPath(Player player, PlayerState state) {
@@ -485,17 +566,43 @@ final class BaseSettingsCommand implements CommandExecutor, TabCompleter {
             List<String> modes = arguments[0].equalsIgnoreCase("visitors")
                 ? VISITOR_MODES
                 : switch (arguments[0].toLowerCase(Locale.ROOT)) {
-                    case "pocket" -> List.of("upgrade", "mobs");
+                    case "pocket" -> List.of("upgrade", "mobs", "type");
                     case "navigation", "flight", "border", "spawnable", "bossbar" -> ENABLE_MODES;
                     default -> List.of();
                 };
             String prefix = arguments[1].toLowerCase(Locale.ROOT);
             return modes.stream().filter(mode -> mode.startsWith(prefix)).toList();
         }
-        if (arguments.length == 3 && arguments[0].equalsIgnoreCase("pocket")
-                && arguments[1].equalsIgnoreCase("mobs")) {
+        if (arguments.length == 3 && arguments[0].equalsIgnoreCase("pocket")) {
             String prefix = arguments[2].toLowerCase(Locale.ROOT);
-            return ENABLE_MODES.stream().filter(mode -> mode.startsWith(prefix)).toList();
+            if (arguments[1].equalsIgnoreCase("mobs")) {
+                return List.of("hostile", "passive").stream()
+                    .filter(category -> category.startsWith(prefix))
+                    .toList();
+            }
+            if (arguments[1].equalsIgnoreCase("type")) {
+                return POCKET_WORLD_TYPES.stream()
+                    .filter(type -> type.startsWith(prefix))
+                    .toList();
+            }
+        }
+        if (arguments.length == 4 && arguments[0].equalsIgnoreCase("pocket")) {
+            String prefix = arguments[3].toLowerCase(Locale.ROOT);
+            if (arguments[1].equalsIgnoreCase("mobs")
+                    && (arguments[2].equalsIgnoreCase("hostile")
+                        || arguments[2].equalsIgnoreCase("passive"))) {
+                return ENABLE_MODES.stream()
+                    .filter(mode -> mode.startsWith(prefix))
+                    .toList();
+            }
+            if (arguments[1].equalsIgnoreCase("type")) {
+                return PocketBaseWorldType.fromCommand(arguments[2])
+                    .map(PocketBaseBiome::commandNames)
+                    .orElse(List.of())
+                    .stream()
+                    .filter(biome -> biome.startsWith(prefix))
+                    .toList();
+            }
         }
         return List.of();
     }
@@ -556,7 +663,9 @@ final class BaseSettingsCommand implements CommandExecutor, TabCompleter {
 
     private static void sendUsage(Player player) {
         player.sendMessage(ChatColor.RED + "Usage: /basesettings "
-            + "[status|upgrade|pocket upgrade|pocket mobs <enable|disable>"
+            + "[status|upgrade|pocket upgrade|pocket mobs "
+            + "<hostile|passive> <enable|disable>"
+            + "|pocket type <void|nether|overworld> <subtype>"
             + "|visitors <allowed|blocked>|navigation <enable|disable>"
             + "|flight <enable|disable>|border <enable|disable>"
             + "|spawnable <enable|disable>|bossbar <enable|disable>]");

src/main/java/games/dmg/spigotbase/PluginSettings.java

@@ -39,12 +39,14 @@ public record PluginSettings(
     int visitorUnlockDiamondCost,
     int pocketBaseUnlockCost,
     int pocketBaseUpgradeCost,
+    int pocketBaseBiomeChangeCost,
     Set<String> baseUnlockMaterials,
     String stoneExpansionMaterial,
     String deepslateExpansionMaterial,
     String obsidianExpansionMaterial,
     String visitorCurrencyMaterial,
     String pocketBaseCurrencyMaterial,
+    String pocketBaseBiomeCurrencyMaterial,
     String pocketBasePortalFrameMaterial,
     Set<String> cooldownExcludedMaterials,
     int bossBarDurationTicks,
@@ -85,6 +87,7 @@ public record PluginSettings(
     private static final int DEFAULT_VISITOR_UNLOCK_DIAMOND_COST = 128;
     private static final int DEFAULT_POCKET_BASE_UNLOCK_COST = 64;
     private static final int DEFAULT_POCKET_BASE_UPGRADE_COST = 16;
+    private static final int DEFAULT_POCKET_BASE_BIOME_CHANGE_COST = 16;
     private static final int DEFAULT_BOSS_BAR_DURATION_TICKS = 60;
     private static final int DEFAULT_NAVIGATION_PARTICLE_COUNT = 5;
     private static final int DEFAULT_TITLE_FADE_IN_TICKS = 10;
@@ -148,6 +151,7 @@ public record PluginSettings(
         requirePositive(visitorUnlockDiamondCost, "visitor-unlock-diamond-cost");
         requirePositive(pocketBaseUnlockCost, "pocket-base-unlock-cost");
         requirePositive(pocketBaseUpgradeCost, "pocket-base-upgrade-cost");
+        requirePositive(pocketBaseBiomeChangeCost, "pocket-base-biome-change-cost");
         baseUnlockMaterials = normalizedSet(baseUnlockMaterials, "base-unlock-materials", false);
         stoneExpansionMaterial = normalizedName(stoneExpansionMaterial, "stone-expansion-material");
         deepslateExpansionMaterial = normalizedName(
@@ -162,6 +166,9 @@ public record PluginSettings(
         pocketBaseCurrencyMaterial = normalizedName(
             pocketBaseCurrencyMaterial, "pocket-base-currency-material"
         );
+        pocketBaseBiomeCurrencyMaterial = normalizedName(
+            pocketBaseBiomeCurrencyMaterial, "pocket-base-biome-currency-material"
+        );
         pocketBasePortalFrameMaterial = normalizedName(
             pocketBasePortalFrameMaterial, "pocket-base-portal-frame-material"
         );
@@ -230,12 +237,18 @@ public record PluginSettings(
             integer(values, "visitor-unlock-diamond-cost", DEFAULT_VISITOR_UNLOCK_DIAMOND_COST),
             integer(values, "pocket-base-unlock-cost", DEFAULT_POCKET_BASE_UNLOCK_COST),
             integer(values, "pocket-base-upgrade-cost", DEFAULT_POCKET_BASE_UPGRADE_COST),
+            integer(
+                values,
+                "pocket-base-biome-change-cost",
+                DEFAULT_POCKET_BASE_BIOME_CHANGE_COST
+            ),
             stringSet(values, "base-unlock-materials", Set.of("GRASS_BLOCK", "DIRT")),
             string(values, "stone-expansion-material", "STONE"),
             string(values, "deepslate-expansion-material", "DEEPSLATE"),
             string(values, "obsidian-expansion-material", "OBSIDIAN"),
             string(values, "visitor-currency-material", "DIAMOND"),
             string(values, "pocket-base-currency-material", "DIAMOND_BLOCK"),
+            string(values, "pocket-base-biome-currency-material", "NETHERITE_BLOCK"),
             string(values, "pocket-base-portal-frame-material", "DIAMOND_BLOCK"),
             stringSet(values, "cooldown-excluded-materials", Set.of()),
             integer(values, "boss-bar-duration-ticks", DEFAULT_BOSS_BAR_DURATION_TICKS),

src/main/java/games/dmg/spigotbase/PluginSettingsValidator.java

@@ -29,6 +29,10 @@ final class PluginSettingsValidator {
         }
         validateCurrency(settings.visitorCurrencyMaterial(), "visitor-currency-material");
         validateCurrency(settings.pocketBaseCurrencyMaterial(), "pocket-base-currency-material");
+        validateCurrency(
+            settings.pocketBaseBiomeCurrencyMaterial(),
+            "pocket-base-biome-currency-material"
+        );
         return settings;
     }
 

src/main/java/games/dmg/spigotbase/PocketBaseBiome.java

@@ -0,0 +1,105 @@
+package games.dmg.spigotbase;
+
+import java.util.Arrays;
+import java.util.List;
+import java.util.Locale;
+import java.util.Optional;
+
+public enum PocketBaseBiome {
+    THE_VOID(PocketBaseWorldType.VOID),
+
+    NETHER_WASTES(PocketBaseWorldType.NETHER),
+    SOUL_SAND_VALLEY(PocketBaseWorldType.NETHER),
+    CRIMSON_FOREST(PocketBaseWorldType.NETHER),
+    WARPED_FOREST(PocketBaseWorldType.NETHER),
+    BASALT_DELTAS(PocketBaseWorldType.NETHER),
+
+    OCEAN(PocketBaseWorldType.OVERWORLD),
+    PLAINS(PocketBaseWorldType.OVERWORLD),
+    DESERT(PocketBaseWorldType.OVERWORLD),
+    WINDSWEPT_HILLS(PocketBaseWorldType.OVERWORLD),
+    FOREST(PocketBaseWorldType.OVERWORLD),
+    TAIGA(PocketBaseWorldType.OVERWORLD),
+    SWAMP(PocketBaseWorldType.OVERWORLD),
+    MANGROVE_SWAMP(PocketBaseWorldType.OVERWORLD),
+    RIVER(PocketBaseWorldType.OVERWORLD),
+    FROZEN_OCEAN(PocketBaseWorldType.OVERWORLD),
+    FROZEN_RIVER(PocketBaseWorldType.OVERWORLD),
+    SNOWY_PLAINS(PocketBaseWorldType.OVERWORLD),
+    MUSHROOM_FIELDS(PocketBaseWorldType.OVERWORLD),
+    BEACH(PocketBaseWorldType.OVERWORLD),
+    JUNGLE(PocketBaseWorldType.OVERWORLD),
+    SPARSE_JUNGLE(PocketBaseWorldType.OVERWORLD),
+    DEEP_OCEAN(PocketBaseWorldType.OVERWORLD),
+    STONY_SHORE(PocketBaseWorldType.OVERWORLD),
+    SNOWY_BEACH(PocketBaseWorldType.OVERWORLD),
+    BIRCH_FOREST(PocketBaseWorldType.OVERWORLD),
+    DARK_FOREST(PocketBaseWorldType.OVERWORLD),
+    PALE_GARDEN(PocketBaseWorldType.OVERWORLD),
+    SNOWY_TAIGA(PocketBaseWorldType.OVERWORLD),
+    OLD_GROWTH_PINE_TAIGA(PocketBaseWorldType.OVERWORLD),
+    WINDSWEPT_FOREST(PocketBaseWorldType.OVERWORLD),
+    SAVANNA(PocketBaseWorldType.OVERWORLD),
+    SAVANNA_PLATEAU(PocketBaseWorldType.OVERWORLD),
+    BADLANDS(PocketBaseWorldType.OVERWORLD),
+    WOODED_BADLANDS(PocketBaseWorldType.OVERWORLD),
+    WARM_OCEAN(PocketBaseWorldType.OVERWORLD),
+    LUKEWARM_OCEAN(PocketBaseWorldType.OVERWORLD),
+    COLD_OCEAN(PocketBaseWorldType.OVERWORLD),
+    DEEP_LUKEWARM_OCEAN(PocketBaseWorldType.OVERWORLD),
+    DEEP_COLD_OCEAN(PocketBaseWorldType.OVERWORLD),
+    DEEP_FROZEN_OCEAN(PocketBaseWorldType.OVERWORLD),
+    SUNFLOWER_PLAINS(PocketBaseWorldType.OVERWORLD),
+    WINDSWEPT_GRAVELLY_HILLS(PocketBaseWorldType.OVERWORLD),
+    FLOWER_FOREST(PocketBaseWorldType.OVERWORLD),
+    ICE_SPIKES(PocketBaseWorldType.OVERWORLD),
+    OLD_GROWTH_BIRCH_FOREST(PocketBaseWorldType.OVERWORLD),
+    OLD_GROWTH_SPRUCE_TAIGA(PocketBaseWorldType.OVERWORLD),
+    WINDSWEPT_SAVANNA(PocketBaseWorldType.OVERWORLD),
+    ERODED_BADLANDS(PocketBaseWorldType.OVERWORLD),
+    BAMBOO_JUNGLE(PocketBaseWorldType.OVERWORLD),
+    DRIPSTONE_CAVES(PocketBaseWorldType.OVERWORLD),
+    LUSH_CAVES(PocketBaseWorldType.OVERWORLD),
+    DEEP_DARK(PocketBaseWorldType.OVERWORLD),
+    SULFUR_CAVES(PocketBaseWorldType.OVERWORLD),
+    MEADOW(PocketBaseWorldType.OVERWORLD),
+    GROVE(PocketBaseWorldType.OVERWORLD),
+    SNOWY_SLOPES(PocketBaseWorldType.OVERWORLD),
+    FROZEN_PEAKS(PocketBaseWorldType.OVERWORLD),
+    JAGGED_PEAKS(PocketBaseWorldType.OVERWORLD),
+    STONY_PEAKS(PocketBaseWorldType.OVERWORLD),
+    CHERRY_GROVE(PocketBaseWorldType.OVERWORLD);
+
+    private final PocketBaseWorldType worldType;
+
+    PocketBaseBiome(PocketBaseWorldType worldType) {
+        this.worldType = worldType;
+    }
+
+    public PocketBaseWorldType worldType() {
+        return worldType;
+    }
+
+    public String commandName() {
+        return name().toLowerCase(Locale.ROOT);
+    }
+
+    static Optional<PocketBaseBiome> fromCommand(
+        PocketBaseWorldType worldType,
+        String value
+    ) {
+        try {
+            PocketBaseBiome biome = valueOf(value.toUpperCase(Locale.ROOT));
+            return biome.worldType == worldType ? Optional.of(biome) : Optional.empty();
+        } catch (IllegalArgumentException exception) {
+            return Optional.empty();
+        }
+    }
+
+    static List<String> commandNames(PocketBaseWorldType worldType) {
+        return Arrays.stream(values())
+            .filter(biome -> biome.worldType == worldType)
+            .map(PocketBaseBiome::commandName)
+            .toList();
+    }
+}

src/main/java/games/dmg/spigotbase/PocketBaseController.java

@@ -79,10 +79,6 @@ final class PocketBaseController implements Listener, Runnable {
         if (pocket.level() < 1) {
             return;
         }
-        PlayerState owner = baseStates.player(player.getUniqueId(), player.getName());
-        if (owner.baseLevel() < 4 || owner.base().isEmpty()) {
-            return;
-        }
         Block clicked = event.getClickedBlock();
         World world = clicked.getWorld();
         Material frameMaterial = Material.valueOf(
@@ -98,6 +94,37 @@ final class PocketBaseController implements Listener, Runnable {
         if (portal.isEmpty()) {
             return;
         }
+        Optional<UUID> pocketOwner = pocketBases.ownerForPocketWorld(world.getUID());
+        if (pocketOwner.isPresent()) {
+            if (!pocketOwner.orElseThrow().equals(player.getUniqueId())) {
+                return;
+            }
+            if (PocketPortalGeometry.frameBlocks(portal.orElseThrow()).stream()
+                    .anyMatch(candidate -> !pocketBases.policy().contains(
+                        pocket.level(), candidate.x(), candidate.z()
+                    ))) {
+                player.sendMessage(ChatColor.RED
+                    + "The complete return portal must be inside your Pocket Base boundary.");
+                event.setCancelled(true);
+                return;
+            }
+            try {
+                pocketBases.activateReturnPortal(player.getUniqueId(), portal.orElseThrow());
+            } catch (IOException | RuntimeException exception) {
+                logger.log(Level.SEVERE, "Could not activate Pocket Base return portal", exception);
+                player.sendMessage(ChatColor.RED
+                    + "The Pocket Base return portal could not be activated.");
+                event.setCancelled(true);
+                return;
+            }
+            event.setCancelled(true);
+            player.sendMessage(ChatColor.GREEN + "Pocket Base return portal activated.");
+            return;
+        }
+        PlayerState owner = baseStates.player(player.getUniqueId(), player.getName());
+        if (owner.baseLevel() < 4 || owner.base().isEmpty()) {
+            return;
+        }
         BaseArea area = baseBounds.area(owner);
         if (PocketPortalGeometry.frameBlocks(portal.orElseThrow()).stream().anyMatch(candidate ->
                 !area.contains(world.getUID(), candidate.x(), candidate.y(), candidate.z()))) {

src/main/java/games/dmg/spigotbase/PocketBaseManager.java

@@ -38,7 +38,7 @@ final class PocketBaseManager {
         PocketBaseState current = states.state(ownerId);
         int nextLevel = Math.addExact(current.level(), 1);
         policy.size(nextLevel);
-        worlds.expand(ownerId, current.level(), nextLevel);
+        worlds.expand(ownerId, current.level(), nextLevel, current.biome());
         return states.updateAndSave(ownerId, state -> state.withLevel(nextLevel));
     }
 
@@ -60,20 +60,80 @@ final class PocketBaseManager {
         }
     }
 
-    PocketBaseState setMobSpawning(UUID ownerId, boolean enabled) throws IOException {
+    PocketBaseState activateReturnPortal(
+        UUID ownerId,
+        PocketPortalLocation portal
+    ) throws IOException {
         PocketBaseState current = states.state(ownerId);
         if (current.level() < 1) {
             throw new IllegalStateException("Pocket Base I is still locked");
         }
-        worlds.setMobSpawning(ownerId, enabled);
+        return states.updateAndSave(ownerId, state -> state.withReturnPortal(portal));
+    }
+
+    PocketBaseState setBiome(UUID ownerId, PocketBaseBiome biome) throws IOException {
+        PocketBaseState current = states.state(ownerId);
+        if (current.level() < 1) {
+            throw new IllegalStateException("Pocket Base I is still locked");
+        }
+        if (current.biome() == biome) {
+            throw new IllegalArgumentException("Pocket Base already uses that biome");
+        }
         try {
-            return states.updateAndSave(
-                ownerId,
-                state -> state.withMobSpawningEnabled(enabled)
-            );
+            worlds.setBiome(ownerId, current.level(), biome);
+            return states.updateAndSave(ownerId, state -> state.withBiome(biome));
         } catch (IOException | RuntimeException exception) {
             try {
-                worlds.setMobSpawning(ownerId, current.mobSpawningEnabled());
+                worlds.setBiome(ownerId, current.level(), current.biome());
+            } catch (RuntimeException rollbackFailure) {
+                exception.addSuppressed(rollbackFailure);
+            }
+            throw exception;
+        }
+    }
+
+    PocketBaseState setHostileMobSpawning(UUID ownerId, boolean enabled)
+            throws IOException {
+        PocketBaseState current = states.state(ownerId);
+        return setMobSpawning(
+            current,
+            enabled,
+            current.passiveMobSpawningEnabled(),
+            state -> state.withHostileMobSpawningEnabled(enabled)
+        );
+    }
+
+    PocketBaseState setPassiveMobSpawning(UUID ownerId, boolean enabled)
+            throws IOException {
+        PocketBaseState current = states.state(ownerId);
+        return setMobSpawning(
+            current,
+            current.hostileMobSpawningEnabled(),
+            enabled,
+            state -> state.withPassiveMobSpawningEnabled(enabled)
+        );
+    }
+
+    private PocketBaseState setMobSpawning(
+        PocketBaseState current,
+        boolean hostileEnabled,
+        boolean passiveEnabled,
+        java.util.function.UnaryOperator<PocketBaseState> update
+    ) throws IOException {
+        if (current.level() < 1) {
+            throw new IllegalStateException("Pocket Base I is still locked");
+        }
+        UUID ownerId = current.ownerId();
+        worlds.setMobSpawning(ownerId, hostileEnabled, passiveEnabled);
+        try {
+            return states.updateAndSave(ownerId, update);
+        } catch (IOException | RuntimeException exception) {
+            try {
+                worlds.setMobSpawning(
+                    ownerId,
+                    current.hostileMobSpawningEnabled(),
+                    current.passiveMobSpawningEnabled()
+                );
             } catch (RuntimeException rollbackFailure) {
                 exception.addSuppressed(rollbackFailure);
             }
@@ -90,11 +150,13 @@ final class PocketBaseManager {
     }
 
     PocketPortalLocation returnPortal(UUID ownerId) {
-        return worlds.returnPortal(ownerId);
+        return states.state(ownerId).returnPortal().orElseGet(
+            () -> worlds.returnPortal(ownerId)
+        );
     }
 
     boolean returnPortalIsIntact(UUID ownerId) {
-        return worlds.returnPortalIsIntact(ownerId);
+        return worlds.returnPortalIsIntact(ownerId, returnPortal(ownerId));
     }
 
     World pocketWorld(UUID ownerId) {

src/main/java/games/dmg/spigotbase/PocketBaseState.java

@@ -7,7 +7,10 @@ public record PocketBaseState(
     UUID ownerId,
     int level,
     Optional<PocketPortalLocation> entrance,
-    boolean mobSpawningEnabled
+    Optional<PocketPortalLocation> returnPortal,
+    boolean hostileMobSpawningEnabled,
+    boolean passiveMobSpawningEnabled,
+    PocketBaseBiome biome
 ) {
     public PocketBaseState {
         if (ownerId == null) {
@@ -17,8 +20,10 @@ public record PocketBaseState(
             throw new IllegalArgumentException("Pocket Base level must not be negative");
         }
         entrance = entrance == null ? Optional.empty() : entrance;
-        if (level == 0 && entrance.isPresent()) {
-            throw new IllegalArgumentException("a locked Pocket Base cannot have an entrance");
+        returnPortal = returnPortal == null ? Optional.empty() : returnPortal;
+        biome = biome == null ? PocketBaseBiome.THE_VOID : biome;
+        if (level == 0 && (entrance.isPresent() || returnPortal.isPresent())) {
+            throw new IllegalArgumentException("a locked Pocket Base cannot have a portal");
         }
     }
 
@@ -27,26 +32,65 @@ public record PocketBaseState(
         int level,
         Optional<PocketPortalLocation> entrance
     ) {
-        this(ownerId, level, entrance, false);
+        this(
+            ownerId, level, entrance, Optional.empty(), false, false,
+            PocketBaseBiome.THE_VOID
+        );
     }
 
     public static PocketBaseState locked(UUID ownerId) {
-        return new PocketBaseState(ownerId, 0, Optional.empty(), false);
+        return new PocketBaseState(
+            ownerId, 0, Optional.empty(), Optional.empty(), false, false,
+            PocketBaseBiome.THE_VOID
+        );
     }
 
     public PocketBaseState withLevel(int newLevel) {
-        return new PocketBaseState(ownerId, newLevel, entrance, mobSpawningEnabled);
+        return new PocketBaseState(
+            ownerId, newLevel, entrance, returnPortal, hostileMobSpawningEnabled,
+            passiveMobSpawningEnabled, biome
+        );
     }
 
     public PocketBaseState withEntrance(PocketPortalLocation portal) {
-        return new PocketBaseState(ownerId, level, Optional.of(portal), mobSpawningEnabled);
+        return new PocketBaseState(
+            ownerId, level, Optional.of(portal), returnPortal,
+            hostileMobSpawningEnabled, passiveMobSpawningEnabled, biome
+        );
     }
 
     public PocketBaseState withoutEntrance() {
-        return new PocketBaseState(ownerId, level, Optional.empty(), mobSpawningEnabled);
+        return new PocketBaseState(
+            ownerId, level, Optional.empty(), returnPortal, hostileMobSpawningEnabled,
+            passiveMobSpawningEnabled, biome
+        );
     }
 
-    public PocketBaseState withMobSpawningEnabled(boolean enabled) {
-        return new PocketBaseState(ownerId, level, entrance, enabled);
+    public PocketBaseState withReturnPortal(PocketPortalLocation portal) {
+        return new PocketBaseState(
+            ownerId, level, entrance, Optional.of(portal), hostileMobSpawningEnabled,
+            passiveMobSpawningEnabled, biome
+        );
+    }
+
+    public PocketBaseState withHostileMobSpawningEnabled(boolean enabled) {
+        return new PocketBaseState(
+            ownerId, level, entrance, returnPortal, enabled,
+            passiveMobSpawningEnabled, biome
+        );
+    }
+
+    public PocketBaseState withPassiveMobSpawningEnabled(boolean enabled) {
+        return new PocketBaseState(
+            ownerId, level, entrance, returnPortal, hostileMobSpawningEnabled,
+            enabled, biome
+        );
+    }
+
+    public PocketBaseState withBiome(PocketBaseBiome selectedBiome) {
+        return new PocketBaseState(
+            ownerId, level, entrance, returnPortal, hostileMobSpawningEnabled,
+            passiveMobSpawningEnabled, selectedBiome
+        );
     }
 }

src/main/java/games/dmg/spigotbase/PocketBaseWorldService.java

@@ -4,11 +4,15 @@ import java.util.HashMap;
 import java.util.Map;
 import java.util.Optional;
 import java.util.UUID;
+import java.util.function.Function;
 import org.bukkit.Location;
 import org.bukkit.Material;
+import org.bukkit.NamespacedKey;
+import org.bukkit.Registry;
 import org.bukkit.Server;
 import org.bukkit.World;
 import org.bukkit.WorldCreator;
+import org.bukkit.block.Biome;
 
 final class PocketBaseWorldService {
     private static final int PLATFORM_Y = 64;
@@ -16,23 +20,47 @@ final class PocketBaseWorldService {
     private final Server server;
     private final PluginSettingsProvider settings;
     private final PocketBasePolicy policy;
+    private final Function<PocketBaseBiome, Biome> biomeResolver;
     private final Map<UUID, UUID> ownersByWorld = new HashMap<>();
 
     PocketBaseWorldService(Server server, PluginSettingsProvider settings) {
+        this(server, settings, biome -> resolveBiome(server, biome));
+    }
+
+    PocketBaseWorldService(
+        Server server,
+        PluginSettingsProvider settings,
+        Function<PocketBaseBiome, Biome> biomeResolver
+    ) {
         this.server = server;
         this.settings = settings;
         this.policy = new PocketBasePolicy(settings);
+        this.biomeResolver = biomeResolver;
     }
 
     void loadExisting(Map<UUID, PocketBaseState> states) {
         for (PocketBaseState state : states.values()) {
             if (state.level() > 0) {
-                setMobSpawning(state.ownerId(), state.mobSpawningEnabled());
+                setBiome(state.ownerId(), state.level(), state.biome());
+                setMobSpawning(
+                    state.ownerId(),
+                    state.hostileMobSpawningEnabled(),
+                    state.passiveMobSpawningEnabled()
+                );
             }
         }
     }
 
     World expand(UUID ownerId, int previousLevel, int newLevel) {
+        return expand(ownerId, previousLevel, newLevel, PocketBaseBiome.THE_VOID);
+    }
+
+    World expand(
+        UUID ownerId,
+        int previousLevel,
+        int newLevel,
+        PocketBaseBiome biome
+    ) {
         World world = ensureWorld(ownerId);
         int newHalfSize = policy.size(newLevel) / 2;
         int previousHalfSize = previousLevel == 0 ? 0 : policy.size(previousLevel) / 2;
@@ -50,6 +78,7 @@ final class PocketBaseWorldService {
                 world.getBlockAt(x, PLATFORM_Y, z).setType(Material.GRASS_BLOCK, false);
             }
         }
+        applyBiome(world, previousLevel, newLevel, biome);
         if (previousLevel == 0) {
             createReturnPortal(world);
             world.setSpawnLocation(0, PLATFORM_Y + 1, 5);
@@ -66,8 +95,18 @@ final class PocketBaseWorldService {
         return ensureWorld(ownerId);
     }
 
-    void setMobSpawning(UUID ownerId, boolean enabled) {
-        ensureWorld(ownerId).setSpawnFlags(enabled, enabled);
+    void setMobSpawning(
+        UUID ownerId,
+        boolean hostileEnabled,
+        boolean passiveEnabled
+    ) {
+        ensureWorld(ownerId).setSpawnFlags(hostileEnabled, passiveEnabled);
+    }
+
+    void setBiome(UUID ownerId, int level, PocketBaseBiome biome) {
+        World world = ensureWorld(ownerId);
+        applyBiome(world, 0, level, biome);
+        world.save();
     }
 
     Location arrival(UUID ownerId) {
@@ -81,9 +120,11 @@ final class PocketBaseWorldService {
         );
     }
 
-    boolean returnPortalIsIntact(UUID ownerId) {
-        PocketPortalLocation portal = returnPortal(ownerId);
+    boolean returnPortalIsIntact(UUID ownerId, PocketPortalLocation portal) {
         World world = ensureWorld(ownerId);
+        if (!portal.worldId().equals(world.getUID())) {
+            return false;
+        }
         Material frame = Material.valueOf(settings.current().pocketBasePortalFrameMaterial());
         return PocketPortalGeometry.frameBlocks(portal).stream()
             .allMatch(position -> world.getBlockAt(
@@ -112,6 +153,40 @@ final class PocketBaseWorldService {
         return world;
     }
 
+    private void applyBiome(
+        World world,
+        int previousLevel,
+        int newLevel,
+        PocketBaseBiome selectedBiome
+    ) {
+        int newHalfSize = policy.size(newLevel) / 2;
+        int previousHalfSize = previousLevel == 0 ? 0 : policy.size(previousLevel) / 2;
+        Biome biome = biomeResolver.apply(selectedBiome);
+        for (int x = -newHalfSize; x < newHalfSize; x += 4) {
+            for (int z = -newHalfSize; z < newHalfSize; z += 4) {
+                boolean previouslyUnlocked = previousLevel > 0
+                    && x >= -previousHalfSize && x < previousHalfSize
+                    && z >= -previousHalfSize && z < previousHalfSize;
+                if (previouslyUnlocked) {
+                    continue;
+                }
+                for (int y = world.getMinHeight(); y < world.getMaxHeight(); y += 4) {
+                    world.setBiome(x, y, z, biome);
+                }
+            }
+        }
+    }
+
+    private static Biome resolveBiome(Server server, PocketBaseBiome selectedBiome) {
+        Registry<Biome> biomeRegistry = server.getRegistry(Biome.class);
+        if (biomeRegistry == null) {
+            throw new IllegalStateException("Biome registry is unavailable");
+        }
+        return biomeRegistry.getOrThrow(
+            NamespacedKey.minecraft(selectedBiome.commandName())
+        );
+    }
+
     private void createReturnPortal(World world) {
         PocketPortalLocation portal = new PocketPortalLocation(
             world.getUID(), world.getName(), -2, PLATFORM_Y + 1, 0, PocketPortalAxis.X

src/main/java/games/dmg/spigotbase/PocketBaseWorldType.java

@@ -0,0 +1,22 @@
+package games.dmg.spigotbase;
+
+import java.util.Locale;
+import java.util.Optional;
+
+public enum PocketBaseWorldType {
+    VOID,
+    NETHER,
+    OVERWORLD;
+
+    public String commandName() {
+        return name().toLowerCase(Locale.ROOT);
+    }
+
+    static Optional<PocketBaseWorldType> fromCommand(String value) {
+        try {
+            return Optional.of(valueOf(value.toUpperCase(Locale.ROOT)));
+        } catch (IllegalArgumentException exception) {
+            return Optional.empty();
+        }
+    }
+}

src/main/java/games/dmg/spigotbase/YamlPocketBaseRepository.java

@@ -43,7 +43,10 @@ public final class YamlPocketBaseRepository {
                     ownerId,
                     level,
                     loadPortal(yaml, path + ".entrance"),
-                    yaml.getBoolean(path + ".mob-spawning-enabled", false)
+                    loadPortal(yaml, path + ".return-portal"),
+                    loadMobPreference(yaml, path, "hostile-mob-spawning-enabled"),
+                    loadMobPreference(yaml, path, "passive-mob-spawning-enabled"),
+                    loadBiome(yaml, path)
                 );
                 states.put(ownerId, state);
             } catch (IllegalArgumentException ignored) {
@@ -62,8 +65,20 @@ public final class YamlPocketBaseRepository {
         for (PocketBaseState state : states.values()) {
             String path = "owners." + state.ownerId();
             yaml.set(path + ".level", state.level());
-            yaml.set(path + ".mob-spawning-enabled", state.mobSpawningEnabled());
+            yaml.set(
+                path + ".hostile-mob-spawning-enabled",
+                state.hostileMobSpawningEnabled()
+            );
+            yaml.set(
+                path + ".passive-mob-spawning-enabled",
+                state.passiveMobSpawningEnabled()
+            );
+            yaml.set(path + ".world-type", state.biome().worldType().commandName());
+            yaml.set(path + ".biome", state.biome().commandName());
             state.entrance().ifPresent(portal -> savePortal(yaml, path + ".entrance", portal));
+            state.returnPortal().ifPresent(portal ->
+                savePortal(yaml, path + ".return-portal", portal)
+            );
         }
         Path temporary = Files.createTempFile(parent, "spigot-base-pocket-", ".yml");
         try {
@@ -83,6 +98,28 @@ public final class YamlPocketBaseRepository {
         }
     }
 
+    private static boolean loadMobPreference(
+        YamlConfiguration yaml,
+        String path,
+        String categoryKey
+    ) {
+        return yaml.getBoolean(
+            path + "." + categoryKey,
+            yaml.getBoolean(path + ".mob-spawning-enabled", false)
+        );
+    }
+
+    private static PocketBaseBiome loadBiome(YamlConfiguration yaml, String path) {
+        String worldTypeName = yaml.getString(path + ".world-type");
+        String biomeName = yaml.getString(path + ".biome");
+        if (worldTypeName == null || biomeName == null) {
+            return PocketBaseBiome.THE_VOID;
+        }
+        return PocketBaseWorldType.fromCommand(worldTypeName)
+            .flatMap(worldType -> PocketBaseBiome.fromCommand(worldType, biomeName))
+            .orElse(PocketBaseBiome.THE_VOID);
+    }
+
     private static Optional<PocketPortalLocation> loadPortal(
         YamlConfiguration yaml,
         String path
@@ -96,7 +133,7 @@ public final class YamlPocketBaseRepository {
         if (worldId == null || worldName == null || axis == null
                 || !yaml.isInt(path + ".x") || !yaml.isInt(path + ".y")
                 || !yaml.isInt(path + ".z")) {
-            throw new IllegalArgumentException("invalid Pocket Base entrance");
+            throw new IllegalArgumentException("invalid Pocket Base portal");
         }
         return Optional.of(new PocketPortalLocation(
             UUID.fromString(worldId),

src/main/resources/config.yml

@@ -50,6 +50,8 @@ visitor-currency-material: DIAMOND
 pocket-base-unlock-cost: 64
 pocket-base-upgrade-cost: 16
 pocket-base-currency-material: DIAMOND_BLOCK
+pocket-base-biome-change-cost: 16
+pocket-base-biome-currency-material: NETHERITE_BLOCK
 pocket-base-portal-frame-material: DIAMOND_BLOCK
 
 # Spawnable block overlay

src/test/java/games/dmg/spigotbase/BaseSettingsCommandTest.java

@@ -100,10 +100,42 @@ final class BaseSettingsCommandTest {
             List.of("mobs"),
             command.onTabComplete(null, null, "basesettings", new String[] {"pocket", "m"})
         );
+        assertEquals(
+            List.of("type"),
+            command.onTabComplete(null, null, "basesettings", new String[] {"pocket", "t"})
+        );
+        assertEquals(
+            List.of("nether"),
+            command.onTabComplete(
+                null, null, "basesettings", new String[] {"pocket", "type", "n"}
+            )
+        );
+        assertEquals(
+            List.of("crimson_forest"),
+            command.onTabComplete(
+                null,
+                null,
+                "basesettings",
+                new String[] {"pocket", "type", "nether", "c"}
+            )
+        );
+        assertEquals(
+            List.of("hostile"),
+            command.onTabComplete(
+                null, null, "basesettings", new String[] {"pocket", "mobs", "h"}
+            )
+        );
+        assertEquals(
+            List.of("passive"),
+            command.onTabComplete(
+                null, null, "basesettings", new String[] {"pocket", "mobs", "p"}
+            )
+        );
         assertEquals(
             List.of("enable"),
             command.onTabComplete(
-                null, null, "basesettings", new String[] {"pocket", "mobs", "e"}
+                null, null, "basesettings",
+                new String[] {"pocket", "mobs", "hostile", "e"}
             )
         );
         for (String setting : List.of("navigation", "flight", "border", "spawnable", "bossbar")) {
@@ -210,20 +242,53 @@ final class BaseSettingsCommandTest {
     }
 
     @Test
-    void pocketOwnerCanEnableNaturalMobSpawning() throws Exception {
+    void pocketOwnerCanPurchaseBiomeChangeWithConfiguredCurrency() throws Exception {
         UUID playerId = UUID.randomUUID();
         Player player = mock(Player.class);
         when(player.getUniqueId()).thenReturn(playerId);
         when(player.getName()).thenReturn("Builder");
+        PlayerInventory inventory = mock(PlayerInventory.class);
+        when(player.getInventory()).thenReturn(inventory);
+        when(inventory.getStorageContents()).thenReturn(new ItemStack[] {
+            new ItemStack(Material.NETHERITE_BLOCK, 16)
+        });
+        BaseStateManager stateManager = mock(BaseStateManager.class);
+        when(stateManager.player(playerId, "Builder"))
+            .thenReturn(PlayerState.newPlayer(playerId, "Builder"));
+        PocketBaseManager pocketBases = mock(PocketBaseManager.class);
+        PocketBaseState current = new PocketBaseState(playerId, 1, java.util.Optional.empty());
+        when(pocketBases.state(playerId)).thenReturn(current);
+        when(pocketBases.setBiome(playerId, PocketBaseBiome.CRIMSON_FOREST))
+            .thenReturn(current.withBiome(PocketBaseBiome.CRIMSON_FOREST));
+        BaseSettingsCommand command = new BaseSettingsCommand(
+            stateManager,
+            new PluginSettingsProvider(PluginSettings.from(Map.of())),
+            mock(BaseFlightController.class),
+            pocketBases
+        );
+
+        command.onCommand(player, null, "basesettings", new String[] {
+            "pocket", "type", "nether", "crimson_forest"
+        });
+
+        verify(pocketBases).setBiome(playerId, PocketBaseBiome.CRIMSON_FOREST);
+        verify(inventory).setStorageContents(any(ItemStack[].class));
+    }
+
+    @Test
+    void selectingCurrentPocketBiomeDoesNotCharge() throws Exception {
+        UUID playerId = UUID.randomUUID();
+        Player player = mock(Player.class);
+        when(player.getUniqueId()).thenReturn(playerId);
+        when(player.getName()).thenReturn("Builder");
+        PlayerInventory inventory = mock(PlayerInventory.class);
+        when(player.getInventory()).thenReturn(inventory);
         BaseStateManager stateManager = mock(BaseStateManager.class);
         when(stateManager.player(playerId, "Builder"))
             .thenReturn(PlayerState.newPlayer(playerId, "Builder"));
         PocketBaseManager pocketBases = mock(PocketBaseManager.class);
         when(pocketBases.state(playerId)).thenReturn(
-            new PocketBaseState(playerId, 1, java.util.Optional.empty(), false)
-        );
-        when(pocketBases.setMobSpawning(playerId, true)).thenReturn(
-            new PocketBaseState(playerId, 1, java.util.Optional.empty(), true)
+            new PocketBaseState(playerId, 1, java.util.Optional.empty())
         );
         BaseSettingsCommand command = new BaseSettingsCommand(
             stateManager,
@@ -232,13 +297,50 @@ final class BaseSettingsCommandTest {
             pocketBases
         );
 
-        command.onCommand(
-            player, null, "basesettings", new String[] {"pocket", "mobs", "enable"}
+        command.onCommand(player, null, "basesettings", new String[] {
+            "pocket", "type", "void", "the_void"
+        });
+
+        verify(pocketBases, never()).setBiome(
+            org.mockito.ArgumentMatchers.eq(playerId),
+            org.mockito.ArgumentMatchers.any(PocketBaseBiome.class)
+        );
+        verify(inventory, never()).setStorageContents(any(ItemStack[].class));
+    }
+
+    @Test
+    void pocketOwnerCanEnableHostileMobSpawningWithoutChangingPassive() throws Exception {
+        UUID playerId = UUID.randomUUID();
+        Player player = mock(Player.class);
+        when(player.getUniqueId()).thenReturn(playerId);
+        when(player.getName()).thenReturn("Builder");
+        BaseStateManager stateManager = mock(BaseStateManager.class);
+        when(stateManager.player(playerId, "Builder"))
+            .thenReturn(PlayerState.newPlayer(playerId, "Builder"));
+        PocketBaseManager pocketBases = mock(PocketBaseManager.class);
+        PocketBaseState current = new PocketBaseState(
+            playerId, 1, java.util.Optional.empty(), java.util.Optional.empty(),
+            false, true, PocketBaseBiome.THE_VOID
+        );
+        when(pocketBases.state(playerId)).thenReturn(current);
+        when(pocketBases.setHostileMobSpawning(playerId, true)).thenReturn(
+            current.withHostileMobSpawningEnabled(true)
+        );
+        BaseSettingsCommand command = new BaseSettingsCommand(
+            stateManager,
+            new PluginSettingsProvider(PluginSettings.from(Map.of())),
+            mock(BaseFlightController.class),
+            pocketBases
         );
 
-        verify(pocketBases).setMobSpawning(playerId, true);
+        command.onCommand(player, null, "basesettings", new String[] {
+            "pocket", "mobs", "hostile", "enable"
+        });
+
+        verify(pocketBases).setHostileMobSpawning(playerId, true);
+        verify(pocketBases, never()).setPassiveMobSpawning(playerId, true);
         verify(player).sendMessage(org.mockito.ArgumentMatchers.<String>argThat(
-            message -> message.contains("mob spawning") && message.contains("enabled")
+            message -> message.contains("hostile mob spawning") && message.contains("enabled")
         ));
     }
 
@@ -253,9 +355,9 @@ final class BaseSettingsCommandTest {
             .thenReturn(PlayerState.newPlayer(playerId, "Builder"));
         PocketBaseManager pocketBases = mock(PocketBaseManager.class);
         when(pocketBases.state(playerId)).thenReturn(
-            new PocketBaseState(playerId, 1, java.util.Optional.empty(), false)
+            new PocketBaseState(playerId, 1, java.util.Optional.empty())
         );
-        when(pocketBases.setMobSpawning(playerId, true))
+        when(pocketBases.setPassiveMobSpawning(playerId, true))
             .thenThrow(new IOException("save failed"));
         BaseSettingsCommand command = new BaseSettingsCommand(
             stateManager,
@@ -264,9 +366,9 @@ final class BaseSettingsCommandTest {
             pocketBases
         );
 
-        command.onCommand(
-            player, null, "basesettings", new String[] {"pocket", "mobs", "enable"}
-        );
+        command.onCommand(player, null, "basesettings", new String[] {
+            "pocket", "mobs", "passive", "enable"
+        });
 
         verify(player).sendMessage(org.mockito.ArgumentMatchers.<String>argThat(
             message -> message.contains("could not be changed")
@@ -294,11 +396,11 @@ final class BaseSettingsCommandTest {
             pocketBases
         );
 
-        command.onCommand(
-            player, null, "basesettings", new String[] {"pocket", "mobs", "enable"}
-        );
+        command.onCommand(player, null, "basesettings", new String[] {
+            "pocket", "mobs", "hostile", "enable"
+        });
 
-        verify(pocketBases, never()).setMobSpawning(playerId, true);
+        verify(pocketBases, never()).setHostileMobSpawning(playerId, true);
         verify(player).sendMessage(org.mockito.ArgumentMatchers.<String>argThat(
             message -> message.contains("Pocket Base I") && message.contains("locked")
         ));
@@ -343,7 +445,7 @@ final class BaseSettingsCommandTest {
     }
 
     @Test
-    void statusDisplaysPocketMobSpawningPreference() {
+    void statusDisplaysPocketMobSpawningPreferences() {
         UUID playerId = UUID.randomUUID();
         Player player = mock(Player.class);
         when(player.getUniqueId()).thenReturn(playerId);
@@ -353,7 +455,10 @@ final class BaseSettingsCommandTest {
             .thenReturn(PlayerState.newPlayer(playerId, "Builder"));
         PocketBaseManager pocketBases = mock(PocketBaseManager.class);
         when(pocketBases.state(playerId)).thenReturn(
-            new PocketBaseState(playerId, 1, java.util.Optional.empty(), false)
+            new PocketBaseState(
+                playerId, 1, java.util.Optional.empty(), java.util.Optional.empty(),
+                true, false, PocketBaseBiome.THE_VOID
+            )
         );
         BaseSettingsCommand command = new BaseSettingsCommand(
             stateManager,
@@ -366,7 +471,9 @@ final class BaseSettingsCommandTest {
 
         verify(player).sendMessage(org.mockito.ArgumentMatchers.<String>argThat(
             message -> message.contains("Pocket Base 1")
-                && message.contains("mob spawning=disabled")
+                && message.contains("type=void/the_void")
+                && message.contains("hostile spawning=enabled")
+                && message.contains("passive spawning=disabled")
         ));
     }
 

src/test/java/games/dmg/spigotbase/PluginSettingsTest.java

@@ -25,6 +25,8 @@ final class PluginSettingsTest {
         assertEquals(16, settings.pocketBaseUpgradeCost());
         assertEquals("DIAMOND_BLOCK", settings.pocketBaseCurrencyMaterial());
         assertEquals("DIAMOND_BLOCK", settings.pocketBasePortalFrameMaterial());
+        assertEquals(16, settings.pocketBaseBiomeChangeCost());
+        assertEquals("NETHERITE_BLOCK", settings.pocketBaseBiomeCurrencyMaterial());
     }
 
     @Test
@@ -33,13 +35,17 @@ final class PluginSettingsTest {
             "pocket-base-unlock-cost", 32,
             "pocket-base-upgrade-cost", 8,
             "pocket-base-currency-material", "EMERALD_BLOCK",
-            "pocket-base-portal-frame-material", "GOLD_BLOCK"
+            "pocket-base-portal-frame-material", "GOLD_BLOCK",
+            "pocket-base-biome-change-cost", 12,
+            "pocket-base-biome-currency-material", "NETHERITE_INGOT"
         ));
 
         assertEquals(32, settings.pocketBaseUnlockCost());
         assertEquals(8, settings.pocketBaseUpgradeCost());
         assertEquals("EMERALD_BLOCK", settings.pocketBaseCurrencyMaterial());
         assertEquals("GOLD_BLOCK", settings.pocketBasePortalFrameMaterial());
+        assertEquals(12, settings.pocketBaseBiomeChangeCost());
+        assertEquals("NETHERITE_INGOT", settings.pocketBaseBiomeCurrencyMaterial());
     }
 
     @Test

src/test/java/games/dmg/spigotbase/PocketBaseControllerTest.java

@@ -2,6 +2,7 @@ package games.dmg.spigotbase;
 
 import static org.mockito.ArgumentMatchers.anyInt;
 import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.never;
 import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.when;
 
@@ -85,6 +86,114 @@ final class PocketBaseControllerTest {
         verify(event).setCancelled(true);
     }
 
+    @Test
+    void ownerCanActivateCompleteReturnFrameInsideOwnPocketBase() throws Exception {
+        UUID ownerId = UUID.randomUUID();
+        UUID worldId = UUID.randomUUID();
+        PocketPortalLocation portal = new PocketPortalLocation(
+            worldId, "pocket", 8, 65, 8, PocketPortalAxis.X
+        );
+        Set<BlockPosition> frame = new HashSet<>(PocketPortalGeometry.frameBlocks(portal));
+        Player owner = mock(Player.class);
+        World world = mock(World.class);
+        Block clicked = block(world, 8, 67, 8, Material.DIAMOND_BLOCK);
+        PlayerInteractEvent event = mock(PlayerInteractEvent.class);
+        PocketBaseManager pocketBases = mock(PocketBaseManager.class);
+        PluginSettings settings = PluginSettings.from(Map.of());
+
+        when(owner.getUniqueId()).thenReturn(ownerId);
+        when(event.getPlayer()).thenReturn(owner);
+        when(event.getAction()).thenReturn(Action.RIGHT_CLICK_BLOCK);
+        when(event.getClickedBlock()).thenReturn(clicked);
+        when(event.getItem()).thenReturn(new ItemStack(Material.FLINT_AND_STEEL));
+        when(world.getUID()).thenReturn(worldId);
+        when(world.getName()).thenReturn("pocket");
+        when(world.getBlockAt(anyInt(), anyInt(), anyInt())).thenAnswer(invocation -> {
+            BlockPosition position = new BlockPosition(
+                invocation.getArgument(0), invocation.getArgument(1), invocation.getArgument(2)
+            );
+            return block(
+                world,
+                position.x(),
+                position.y(),
+                position.z(),
+                frame.contains(position) ? Material.DIAMOND_BLOCK : Material.AIR
+            );
+        });
+        when(pocketBases.ownerForPocketWorld(worldId)).thenReturn(Optional.of(ownerId));
+        when(pocketBases.state(ownerId)).thenReturn(
+            new PocketBaseState(ownerId, 1, Optional.empty())
+        );
+        when(pocketBases.policy()).thenReturn(new PocketBasePolicy(settings));
+        PocketBaseController controller = new PocketBaseController(
+            mock(Server.class),
+            mock(BaseStateManager.class),
+            new BaseBoundsService(settings),
+            pocketBases,
+            new PluginSettingsProvider(settings),
+            Logger.getAnonymousLogger()
+        );
+
+        controller.onActivate(event);
+
+        verify(pocketBases).activateReturnPortal(ownerId, portal);
+        verify(event).setCancelled(true);
+    }
+
+    @Test
+    void returnFrameOutsideUnlockedPocketBoundaryIsRejected() throws Exception {
+        UUID ownerId = UUID.randomUUID();
+        UUID worldId = UUID.randomUUID();
+        PocketPortalLocation portal = new PocketPortalLocation(
+            worldId, "pocket", 30, 65, 8, PocketPortalAxis.X
+        );
+        Set<BlockPosition> frame = new HashSet<>(PocketPortalGeometry.frameBlocks(portal));
+        Player owner = mock(Player.class);
+        World world = mock(World.class);
+        Block clicked = block(world, 30, 67, 8, Material.DIAMOND_BLOCK);
+        PlayerInteractEvent event = mock(PlayerInteractEvent.class);
+        PocketBaseManager pocketBases = mock(PocketBaseManager.class);
+        PluginSettings settings = PluginSettings.from(Map.of());
+
+        when(owner.getUniqueId()).thenReturn(ownerId);
+        when(event.getPlayer()).thenReturn(owner);
+        when(event.getAction()).thenReturn(Action.RIGHT_CLICK_BLOCK);
+        when(event.getClickedBlock()).thenReturn(clicked);
+        when(event.getItem()).thenReturn(new ItemStack(Material.FLINT_AND_STEEL));
+        when(world.getUID()).thenReturn(worldId);
+        when(world.getName()).thenReturn("pocket");
+        when(world.getBlockAt(anyInt(), anyInt(), anyInt())).thenAnswer(invocation -> {
+            BlockPosition position = new BlockPosition(
+                invocation.getArgument(0), invocation.getArgument(1), invocation.getArgument(2)
+            );
+            return block(
+                world,
+                position.x(),
+                position.y(),
+                position.z(),
+                frame.contains(position) ? Material.DIAMOND_BLOCK : Material.AIR
+            );
+        });
+        when(pocketBases.ownerForPocketWorld(worldId)).thenReturn(Optional.of(ownerId));
+        when(pocketBases.state(ownerId)).thenReturn(
+            new PocketBaseState(ownerId, 1, Optional.empty())
+        );
+        when(pocketBases.policy()).thenReturn(new PocketBasePolicy(settings));
+        PocketBaseController controller = new PocketBaseController(
+            mock(Server.class),
+            mock(BaseStateManager.class),
+            new BaseBoundsService(settings),
+            pocketBases,
+            new PluginSettingsProvider(settings),
+            Logger.getAnonymousLogger()
+        );
+
+        controller.onActivate(event);
+
+        verify(pocketBases, never()).activateReturnPortal(ownerId, portal);
+        verify(event).setCancelled(true);
+    }
+
     @Test
     void placementOutsideUnlockedPocketBoundaryIsCancelled() {
         UUID ownerId = UUID.randomUUID();

src/test/java/games/dmg/spigotbase/PocketBaseManagerTest.java

@@ -1,5 +1,6 @@
 package games.dmg.spigotbase;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.mockito.Mockito.inOrder;
 import static org.mockito.Mockito.mock;
@@ -16,9 +17,54 @@ import org.mockito.InOrder;
 
 final class PocketBaseManagerTest {
     @Test
-    void persistsAndAppliesMobSpawningPreference() throws Exception {
+    void relocatedReturnPortalOverridesGeneratedDefault() {
         UUID ownerId = UUID.randomUUID();
-        PocketBaseState current = new PocketBaseState(ownerId, 1, Optional.empty(), false);
+        PocketPortalLocation relocated = new PocketPortalLocation(
+            UUID.randomUUID(), "pocket", 20, 65, 12, PocketPortalAxis.Z
+        );
+        PocketBaseStateManager states = mock(PocketBaseStateManager.class);
+        PocketBaseWorldService worlds = mock(PocketBaseWorldService.class);
+        when(states.state(ownerId)).thenReturn(new PocketBaseState(
+            ownerId, 1, Optional.empty(), Optional.of(relocated), false, false,
+            PocketBaseBiome.THE_VOID
+        ));
+        PocketBaseManager manager = new PocketBaseManager(
+            states,
+            worlds,
+            new PluginSettingsProvider(PluginSettings.from(Map.of()))
+        );
+
+        assertEquals(relocated, manager.returnPortal(ownerId));
+    }
+
+    @Test
+    void existingStateWithoutRelocationUsesGeneratedReturnPortal() {
+        UUID ownerId = UUID.randomUUID();
+        PocketPortalLocation generated = new PocketPortalLocation(
+            UUID.randomUUID(), "pocket", -2, 65, 0, PocketPortalAxis.X
+        );
+        PocketBaseStateManager states = mock(PocketBaseStateManager.class);
+        PocketBaseWorldService worlds = mock(PocketBaseWorldService.class);
+        when(states.state(ownerId)).thenReturn(
+            new PocketBaseState(ownerId, 1, Optional.empty())
+        );
+        when(worlds.returnPortal(ownerId)).thenReturn(generated);
+        PocketBaseManager manager = new PocketBaseManager(
+            states,
+            worlds,
+            new PluginSettingsProvider(PluginSettings.from(Map.of()))
+        );
+
+        assertEquals(generated, manager.returnPortal(ownerId));
+    }
+
+    @Test
+    void persistsAndAppliesHostileMobSpawningWithoutChangingPassive() throws Exception {
+        UUID ownerId = UUID.randomUUID();
+        PocketBaseState current = new PocketBaseState(
+            ownerId, 1, Optional.empty(), Optional.empty(), false, true,
+            PocketBaseBiome.THE_VOID
+        );
         PocketBaseStateManager states = mock(PocketBaseStateManager.class);
         PocketBaseWorldService worlds = mock(PocketBaseWorldService.class);
         when(states.state(ownerId)).thenReturn(current);
@@ -34,19 +80,50 @@ final class PocketBaseManagerTest {
             new PluginSettingsProvider(PluginSettings.from(Map.of()))
         );
 
-        manager.setMobSpawning(ownerId, true);
+        PocketBaseState updated = manager.setHostileMobSpawning(ownerId, true);
 
+        assertEquals(true, updated.hostileMobSpawningEnabled());
+        assertEquals(true, updated.passiveMobSpawningEnabled());
         InOrder order = inOrder(worlds, states);
-        order.verify(worlds).setMobSpawning(ownerId, true);
+        order.verify(worlds).setMobSpawning(ownerId, true, true);
         order.verify(states).updateAndSave(
             org.mockito.ArgumentMatchers.eq(ownerId), org.mockito.ArgumentMatchers.any()
         );
     }
 
     @Test
-    void restoresWorldSettingWhenPersistenceFails() throws Exception {
+    void persistsBiomeAfterApplyingItToTheUnlockedArea() throws Exception {
         UUID ownerId = UUID.randomUUID();
-        PocketBaseState current = new PocketBaseState(ownerId, 1, Optional.empty(), false);
+        PocketBaseState current = new PocketBaseState(ownerId, 2, Optional.empty());
+        PocketBaseStateManager states = mock(PocketBaseStateManager.class);
+        PocketBaseWorldService worlds = mock(PocketBaseWorldService.class);
+        when(states.state(ownerId)).thenReturn(current);
+        when(states.updateAndSave(org.mockito.ArgumentMatchers.eq(ownerId),
+            org.mockito.ArgumentMatchers.any())).thenAnswer(invocation -> {
+                @SuppressWarnings("unchecked")
+                UnaryOperator<PocketBaseState> operation = invocation.getArgument(1);
+                return operation.apply(current);
+            });
+        PocketBaseManager manager = new PocketBaseManager(
+            states,
+            worlds,
+            new PluginSettingsProvider(PluginSettings.from(Map.of()))
+        );
+
+        PocketBaseState updated = manager.setBiome(ownerId, PocketBaseBiome.WARPED_FOREST);
+
+        assertEquals(PocketBaseBiome.WARPED_FOREST, updated.biome());
+        InOrder order = inOrder(worlds, states);
+        order.verify(worlds).setBiome(ownerId, 2, PocketBaseBiome.WARPED_FOREST);
+        order.verify(states).updateAndSave(
+            org.mockito.ArgumentMatchers.eq(ownerId), org.mockito.ArgumentMatchers.any()
+        );
+    }
+
+    @Test
+    void restoresPreviousBiomeWhenPersistenceFails() throws Exception {
+        UUID ownerId = UUID.randomUUID();
+        PocketBaseState current = new PocketBaseState(ownerId, 1, Optional.empty());
         PocketBaseStateManager states = mock(PocketBaseStateManager.class);
         PocketBaseWorldService worlds = mock(PocketBaseWorldService.class);
         when(states.state(ownerId)).thenReturn(current);
@@ -58,9 +135,35 @@ final class PocketBaseManagerTest {
             new PluginSettingsProvider(PluginSettings.from(Map.of()))
         );
 
-        assertThrows(IOException.class, () -> manager.setMobSpawning(ownerId, true));
+        assertThrows(IOException.class,
+            () -> manager.setBiome(ownerId, PocketBaseBiome.DESERT));
 
-        verify(worlds).setMobSpawning(ownerId, true);
-        verify(worlds).setMobSpawning(ownerId, false);
+        verify(worlds).setBiome(ownerId, 1, PocketBaseBiome.DESERT);
+        verify(worlds).setBiome(ownerId, 1, PocketBaseBiome.THE_VOID);
+    }
+
+    @Test
+    void restoresBothWorldSettingsWhenPersistenceFails() throws Exception {
+        UUID ownerId = UUID.randomUUID();
+        PocketBaseState current = new PocketBaseState(
+            ownerId, 1, Optional.empty(), Optional.empty(), true, false,
+            PocketBaseBiome.THE_VOID
+        );
+        PocketBaseStateManager states = mock(PocketBaseStateManager.class);
+        PocketBaseWorldService worlds = mock(PocketBaseWorldService.class);
+        when(states.state(ownerId)).thenReturn(current);
+        when(states.updateAndSave(org.mockito.ArgumentMatchers.eq(ownerId),
+            org.mockito.ArgumentMatchers.any())).thenThrow(new IOException("save failed"));
+        PocketBaseManager manager = new PocketBaseManager(
+            states,
+            worlds,
+            new PluginSettingsProvider(PluginSettings.from(Map.of()))
+        );
+
+        assertThrows(IOException.class,
+            () -> manager.setPassiveMobSpawning(ownerId, true));
+
+        verify(worlds).setMobSpawning(ownerId, true, true);
+        verify(worlds).setMobSpawning(ownerId, true, false);
     }
 }

src/test/java/games/dmg/spigotbase/PocketBaseWorldServiceTest.java

@@ -1,6 +1,8 @@
 package games.dmg.spigotbase;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.never;
@@ -29,9 +31,12 @@ final class PocketBaseWorldServiceTest {
         when(server.createWorld(any(WorldCreator.class))).thenReturn(world);
         when(world.getUID()).thenReturn(worldId);
         when(world.getName()).thenReturn("pocket");
+        when(world.getMinHeight()).thenReturn(0);
+        when(world.getMaxHeight()).thenReturn(8);
         PocketBaseWorldService service = new PocketBaseWorldService(
             server,
-            new PluginSettingsProvider(PluginSettings.from(Map.of()))
+            new PluginSettingsProvider(PluginSettings.from(Map.of())),
+            ignored -> null
         );
 
         service.expand(ownerId, 0, 1);
@@ -46,6 +51,33 @@ final class PocketBaseWorldServiceTest {
         assertEquals(ownerId, service.ownerForWorld(worldId).orElseThrow());
     }
 
+    @Test
+    void checksRelocatedReturnPortalFrameAtItsSavedLocation() {
+        UUID ownerId = UUID.randomUUID();
+        UUID worldId = UUID.randomUUID();
+        Server server = mock(Server.class);
+        World world = mock(World.class);
+        Map<BlockPosition, Block> blocks = blocks(world);
+        when(server.getWorld(org.mockito.ArgumentMatchers.anyString())).thenReturn(world);
+        when(world.getUID()).thenReturn(worldId);
+        PocketPortalLocation portal = new PocketPortalLocation(
+            worldId, "pocket", 20, 65, 12, PocketPortalAxis.Z
+        );
+        for (BlockPosition position : PocketPortalGeometry.frameBlocks(portal)) {
+            when(world.getBlockAt(position.x(), position.y(), position.z()).getType())
+                .thenReturn(Material.DIAMOND_BLOCK);
+        }
+        PocketBaseWorldService service = new PocketBaseWorldService(
+            server,
+            new PluginSettingsProvider(PluginSettings.from(Map.of()))
+        );
+
+        assertTrue(service.returnPortalIsIntact(ownerId, portal));
+
+        when(world.getBlockAt(20, 65, 12).getType()).thenReturn(Material.AIR);
+        assertFalse(service.returnPortalIsIntact(ownerId, portal));
+    }
+
     @Test
     void reappliesSavedMobSpawningPreferenceWhenWorldLoads() {
         UUID ownerId = UUID.randomUUID();
@@ -55,15 +87,45 @@ final class PocketBaseWorldServiceTest {
         when(world.getUID()).thenReturn(UUID.randomUUID());
         PocketBaseWorldService service = new PocketBaseWorldService(
             server,
-            new PluginSettingsProvider(PluginSettings.from(Map.of()))
+            new PluginSettingsProvider(PluginSettings.from(Map.of())),
+            ignored -> null
         );
 
         service.loadExisting(Map.of(
             ownerId,
-            new PocketBaseState(ownerId, 1, Optional.empty(), true)
+            new PocketBaseState(
+                ownerId, 1, Optional.empty(), Optional.empty(), true, false,
+                PocketBaseBiome.THE_VOID
+            )
         ));
 
-        verify(world).setSpawnFlags(true, true);
+        verify(world).setSpawnFlags(true, false);
+    }
+
+    @Test
+    void appliesSelectedBiomeAcrossUnlockedColumnsWithoutChangingBlocks() {
+        UUID ownerId = UUID.randomUUID();
+        Server server = mock(Server.class);
+        World world = mock(World.class);
+        when(server.getWorld(org.mockito.ArgumentMatchers.anyString())).thenReturn(world);
+        when(world.getUID()).thenReturn(UUID.randomUUID());
+        when(world.getMinHeight()).thenReturn(0);
+        when(world.getMaxHeight()).thenReturn(8);
+        PocketBaseWorldService service = new PocketBaseWorldService(
+            server,
+            new PluginSettingsProvider(PluginSettings.from(Map.of())),
+            ignored -> null
+        );
+
+        service.setBiome(ownerId, 1, PocketBaseBiome.CRIMSON_FOREST);
+
+        verify(world).setBiome(-32, 0, -32, null);
+        verify(world).setBiome(28, 4, 28, null);
+        verify(world, never()).getBlockAt(
+            org.mockito.ArgumentMatchers.anyInt(),
+            org.mockito.ArgumentMatchers.anyInt(),
+            org.mockito.ArgumentMatchers.anyInt()
+        );
     }
 
     @Test
@@ -75,9 +137,12 @@ final class PocketBaseWorldServiceTest {
         when(server.createWorld(any(WorldCreator.class))).thenReturn(world);
         when(world.getUID()).thenReturn(UUID.randomUUID());
         when(world.getName()).thenReturn("pocket");
+        when(world.getMinHeight()).thenReturn(0);
+        when(world.getMaxHeight()).thenReturn(8);
         PocketBaseWorldService service = new PocketBaseWorldService(
             server,
-            new PluginSettingsProvider(PluginSettings.from(Map.of()))
+            new PluginSettingsProvider(PluginSettings.from(Map.of())),
+            ignored -> null
         );
         Block existingCenter = world.getBlockAt(0, 64, 0);
 
@@ -87,6 +152,8 @@ final class PocketBaseWorldServiceTest {
             .setType(Material.GRASS_BLOCK, false);
         verify(existingCenter, never())
             .setType(any(Material.class), org.mockito.ArgumentMatchers.anyBoolean());
+        verify(world).setBiome(44, 4, 44, null);
+        verify(world, never()).setBiome(0, 0, 0, null);
     }
 
     private static Map<BlockPosition, Block> blocks(World world) {

src/test/java/games/dmg/spigotbase/YamlPocketBaseRepositoryTest.java

@@ -2,6 +2,7 @@ package games.dmg.spigotbase;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import java.nio.file.Files;
 import java.nio.file.Path;
@@ -25,7 +26,12 @@ final class YamlPocketBaseRepositoryTest {
             Optional.of(new PocketPortalLocation(
                 worldId, "world", 10, 65, -4, PocketPortalAxis.X
             )),
-            true
+            Optional.of(new PocketPortalLocation(
+                worldId, "pocket", 20, 65, 12, PocketPortalAxis.Z
+            )),
+            true,
+            false,
+            PocketBaseBiome.CRIMSON_FOREST
         );
         YamlPocketBaseRepository repository = new YamlPocketBaseRepository(
             temporaryDirectory.resolve("pocket-bases.yml")
@@ -43,6 +49,25 @@ final class YamlPocketBaseRepositoryTest {
         Files.writeString(stateFile, "owners:\n  " + ownerId + ":\n    level: 1\n");
         YamlPocketBaseRepository repository = new YamlPocketBaseRepository(stateFile);
 
-        assertFalse(repository.load().get(ownerId).mobSpawningEnabled());
+        PocketBaseState loaded = repository.load().get(ownerId);
+
+        assertFalse(loaded.hostileMobSpawningEnabled());
+        assertFalse(loaded.passiveMobSpawningEnabled());
+        assertTrue(loaded.returnPortal().isEmpty());
+        assertEquals(PocketBaseBiome.THE_VOID, loaded.biome());
+    }
+
+    @Test
+    void migratesLegacyMobPreferenceToBothCategories() throws Exception {
+        UUID ownerId = UUID.randomUUID();
+        Path stateFile = temporaryDirectory.resolve("pocket-bases.yml");
+        Files.writeString(stateFile, "owners:\n  " + ownerId
+            + ":\n    level: 1\n    mob-spawning-enabled: true\n");
+        YamlPocketBaseRepository repository = new YamlPocketBaseRepository(stateFile);
+
+        PocketBaseState loaded = repository.load().get(ownerId);
+
+        assertTrue(loaded.hostileMobSpawningEnabled());
+        assertTrue(loaded.passiveMobSpawningEnabled());
     }
 }