Gray Merchant of Asphodel is a rare Creature — Zombie card from Secret Lair Countdown (SLC), collector number 7. Current market price: $8.51 (foil $15.46), TCGplayer market prices via Scryfall.
When this creature enters, each opponent loses X life, where X is your devotion to black. You gain life equal to the life lost this way. (Each {B} in the mana costs of permanents you control counts toward your devotion to black.)