The mutations are both physical and in abilities. Each new mutant is now significantly stronger and has new, more powerful attacks. They could be considered boss mobs now and would probably work exceptionally well if implemented in an adventure mode game.
Item Spawner IDs
Mutant Creeper Spawner - 458
Mutant Enderman Spawner - 459
Mutant Zombie Spawner - 460
Mutant Skeleton Spawner - 461
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