Mineshaft expansion

What it adds

• Two new mineshaft variants (corrupted and reinforced) that spawn more often and come with heavier monster spawn lists. Loot in any mineshaft chest is richer thanks to added pools (high-tier gear, utility, and explosives).
• New biome Порча (Porcha): a corrupted cave-like overworld biome with dripstone, sculk growths, lava pockets, and hostile-heavy spawns (cave spiders, husks, endermen, rare wardens). The biome is injected into the overworld climate so it can appear naturally.
• Porcha is eligible for vanilla mineshafts and the new mineshaft variants. Custom structure sets control where the variants appear, tied to biome tags.

Implementation notes

• Worldgen is data-driven (structure JSON, structure sets, biome tags, biome JSON) under the mod data pack. A built-in resource/data pack descriptor is included for 1.21.1 formats.
• The mod reflects into the overworld multi-noise preset to add the Порча biome without replacing vanilla files. If reflection fails, generation falls back to vanilla and logs an error.
• Additional mob spawns are injected via Fabric biome modifications for mineshaft biomes and the new biome to raise danger.
• Loot upgrades are applied via LootTableEvents.MODIFY to the abandoned mineshaft chest table.

Usage

• Install the JAR on the client (singleplayer or when connecting to a server with matching worldgen). New worlds will occasionally generate Порча biomes; mineshaft variants can be found in tagged underground biomes (including Порча) and have stronger monster presence and better chests.

Known limitations and future ideas

• Reflection-based biome injection may conflict with other mods that deeply rewrite the overworld preset. If another mod replaces the preset entirely, Порча might not appear.
• Biome rarity is modest to keep worlds close to vanilla; adjust structure set frequencies or the climate window in code for denser corruption.
• Loot boosts affect all mineshafts, not only the new variants; separating tables would require custom structure pieces.