Prosper, Tome-Bound is a mythic Legendary Creature — Tiefling Warlock card from Alchemy Horizons: Baldur's Gate (HBG), collector number 247.
Deathtouch Mystic Arcanum — At the beginning of your end step, exile the top card of your library. Until the end of your next turn, you may play that card. Pact Boon — Whenever you play a card from exile, create a Treasure token.