Xzaraku, Apex of All

Mutate {1}{g/u}{g/u}{w/b}{w/b} (If you cast this spell for its mutate cost, put it over or under target non-Human creature you own. They mutate into the creature on top plus all abilities from under it.)
Menace
Whenever this creature or another creature you control mutates, put 2 times X +1/+1 counters on that creature, where X is the number of times it has mutated.