The Trivia Mastermind is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

, : Look at the top three cards of your library. Choose one of them that isn't a playtest card and say its name, then choose a category among power, toughness, or mana value. An opponent guesses in that category about that card, then reveal the card. If they guessed incorrectly, put the card into your hand. Then, put each card not put into your hand this way on the bottom of your library in any order.