Thassa's Oracle is a rare Creature — Merfolk Wizard card from Secret Lair Drop (SLD), collector number 1280. Current market price: $116.60 (foil $195.50), TCGplayer market prices via Scryfall.
When this creature enters, look at the top X cards of your library, where X is your devotion to blue. Put up to one of them on top of your library and the rest on the bottom of your library in a random order. If X is greater than or equal to the number of cards in your library, you win the game. (Each {U} in the mana costs of permanents you control counts toward your devotion to blue.)