This is a very neat command block that adds a whole new dynamic to mobs in Minecraft. Mutant Creatures Command Block allows for rare but random spawns of mutated mobs. 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.
For Minecraft 1.10.2 and 1.9.4