Sol'kanar the Swamp King is a rare Legendary Creature — Demon card from Dominaria Remastered (DMR), collector number 368. Current market price: $0.31 (foil $0.17), TCGplayer market prices via Scryfall.
Swampwalk (This creature can't be blocked as long as defending player controls a Swamp.) Whenever a player casts a black spell, you gain 1 life.