VOID-ROT

A Fabric 1.21.1 mod that slowly corrupts your world: blocks near a
“corruption source” randomly scramble into a decayed palette (netherrack,
obsidian, sculk, gravel, cracked stone…), sometimes crumble into air, and
the corruption spreads outward over time like a plague eating through the
terrain. Occasionally it triggers glitch events near the frontier: lightning,
particle bursts, weird sounds, entities getting nudged/teleported and given
random status effects, and (rarely) hostile mobs getting swapped for a
different mob entirely.