Protean Hydra
{X}{G}Creature — Hydra
This creature enters with X +1/+1 counters on it. If damage would be dealt to this creature, prevent that damage and remove that many +1/+1 counters from it. Whenever a +1/+1 counter is removed from this creature, put two +1/+1 counters on it at the beginning of the next end step.