Critter, The Worm Virus

Mutate {7} (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.)

Whenever this creature mutates, it gains +6/0 until end
of turn and it is sacrificed at the end of that turn.

When this creature is sacrificed, mutate all cards with mutate from it this creature onto another target creature
you control.