Clockwork Hydra is a uncommon Artifact Creature — Hydra card from Duel Decks: Elspeth vs. Tezzeret (DDF), collector number 55. Current market price: $0.28, TCGplayer market prices via Scryfall.
This creature enters with four +1/+1 counters on it. Whenever this creature attacks or blocks, remove a +1/+1 counter from it. If you do, it deals 1 damage to any target. {T}: Put a +1/+1 counter on this creature.