Allure of the Unknown is a rare Sorcery card from Theros Beyond Death Promos (PTHB), collector number 207p. Current market price: $0.14 (foil $0.21), TCGplayer market prices via Scryfall.
Reveal the top six cards of your library. An opponent exiles a nonland card from among them, then you put the rest into your hand. That opponent may cast the exiled card without paying its mana cost.