Gristleback is a uncommon Creature — Boar Beast card from Guildpact (GPT), collector number 87. Current market price: $0.16 (foil $0.45), TCGplayer market prices via Scryfall.
Bloodthirst 1 (If an opponent was dealt damage this turn, this creature enters with a +1/+1 counter on it.) Sacrifice this creature: You gain life equal to this creature's power.