Grimgrin, Corpse-Born is a mythic Legendary Creature — Zombie Warrior card from Innistrad (ISD), collector number 214. Current market price: $2.38 (foil $9.16), TCGplayer market prices via Scryfall.
Grimgrin enters tapped and doesn't untap during your untap step. Sacrifice another creature: Untap Grimgrin and put a +1/+1 counter on it. Whenever Grimgrin attacks, destroy target creature defending player controls, then put a +1/+1 counter on Grimgrin.