Muk

Muk enters the battlefield with three +1/+1 counters on it.
Poison X (Whenever Muk deals combat damage to a creature, put X -1/-1 counters on that creature, where X is Muks power.)
If damage would be dealt to Muk while it has a +1/+1 counter on it, prevent that damage and remove a +1/+1 counter from it.