Essence Corrupter

Mutate {b}{b}{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.)
Flying, deathtouch
At the beginning of each upkeep, put a -1/-1
counter on Essence Corrupter. Then, you gain
life equal to the number of counters on it.