Gray Merchant of Asphodel is a special Creature — Zombie card from Time Spiral Remastered (TSR), collector number 323. Current market price: $8.31 (foil $91.23), 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.)