Protean Hydra is a mythic Creature — Hydra card from Magic 2010 (M10), collector number 200. Current market price: $4.71 (foil $15.36), TCGplayer market prices via Scryfall.
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.