For every 21 zombies, a skibidi toilet is generated with the head of the player closest to its spawn, these are much stronger and have much more life than a zombie
Skibidi Toilet Datapack
MC 1.21.2-Snapshot, 1.21, 1.21.1-Snapshot, 1.21.4, 1.21.5-Snapshot, 1.21.3, 1.21.1, 1.21.4-Snapshot, 1.21.2