Mortem

Mortem is a difficulty mod for Fabric. Its main hostile mobs (skeletons, spiders, creepers and zombies) get a longer detection range, and a zombie can infect other mobs. The infection chance falls as a mob's armor rises, and a cured mob can return to normal. Villagers and zombies also attack animals and crops. Creepers stop walking once they start to ignite, and the distance at which they ignite is shorter than in vanilla, lowered from 7 to 4. Creepers take explosion damage themselves.

The mod adds a set of mechanics on top of the existing mobs. Skeletons can spawn without bows, and a skeleton has a 30% chance to carry a wither skull effect when killed by a wither. Spiders take fall damage, have a 33% chance to leave cobwebs when hit, and can leap toward a player with webs. Slimes spawn naturally, and endermen have a 33% chance to teleport a victim who hits them. Players who try to eat food while being attacked have the action cancelled. The mod is client and server, so the server and every player need it, and it requires Fabric API.