Rakdos, Lord of Riots is a mythic Legendary Creature — Demon card from RNA Guild Kit (GK2), collector number 52. Current market price: — (foil $5.85), 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.