Greven, Predator Captain is a mythic Legendary Creature — Phyrexian Human Warrior card from Commander 2019 (C19), collector number 43. Current market price: — (foil $0.36), TCGplayer market prices via Scryfall.
Menace Greven gets +X/+0, where X is the amount of life you've lost this turn. Whenever Greven attacks, you may sacrifice another creature. If you do, you draw cards equal to that creature's power and you lose life equal to that creature's toughness.