Rock Hydra is a rare Creature — Hydra card from Revised Edition (3ED), collector number 173. Current market price: $3.87, TCGplayer market prices via Scryfall.
This creature enters with X +1/+1 counters on it. For each 1 damage that would be dealt to this creature, if it has a +1/+1 counter on it, remove a +1/+1 counter from it and prevent that 1 damage. {R}: Prevent the next 1 damage that would be dealt to this creature this turn. {R}{R}{R}: Put a +1/+1 counter on this creature. Activate only during your upkeep.