Allure of the Unknown is a rare Sorcery card from Theros Beyond Death (THB), collector number 207. Current market price: $0.21 (foil $0.10), 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.