Venom

Mutate {3}{u}{u}{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.)

Infect (This creature deals damage to creatures in the form of -1/-1 counters and to players in the form of poison counters.)

If a player has gained five or more poison counters this turn, remove Venom from the battlefield and return him transformed.