Rakdos, Lord of Riots is a rare Legendary Creature — Demon card from Ravnica Remastered (RVR), collector number 379. Current market price: $0.68 (foil $0.83), TCGplayer market prices via Scryfall.
You can't cast Rakdos unless an opponent lost life this turn. Flying, trample Creature spells you cast cost {1} less to cast for each 1 life your opponents have lost this turn.