Sol'kanar the Swamp King is a special Legendary Creature — Demon card from Time Spiral Timeshifted (TSB), collector number 100. Current market price: $0.36 (foil $11.60), 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.