Remove Superflat Slimes

Superflat worlds sit below Y=40 almost everywhere, so every slime chunk turns into a slime farm you never asked for. This mod adds a single game rule that switches those natural spawns off.

The rule is removesuperflatslimes:removesuperflatslimes and it defaults to true, so slimes are gone the moment you install the mod — there is nothing to turn on. Set it to false if you want vanilla behaviour back. The rule also appears in the game rule list when you create a world, under Spawning.

Only natural spawning is affected. Ordinary spawning and the mobs added while chunks generate are blocked. Everything else keeps working exactly as it does in vanilla: spawn eggs, the summon command, monster spawners and trial spawners, and a big slime splitting into smaller ones when you kill it.

The rule applies only to dimensions that use a flat chunk generator, which covers every superflat preset. Normal worlds are untouched, and so are the Nether and the End inside a superflat save, since they use their own generators.

Compatibility: both mixins are plain injections at the head of checkSpawnRules, with no overwrites and no redirects, so nothing is rewritten and other mods can hook the same methods freely. Slimes are matched by class, which means modded slimes extending the vanilla one are covered too. Magma cubes sit on a separate branch of the hierarchy and are not affected.

Requires Minecraft 26.2, Fabric Loader and Fabric API. The mod belongs on the server, or in singleplayer — it is harmless on a client but does nothing there on its own.