Bran, the Three-Eyed Raven

At the beginning of each opponent's upkeep you may look at the top card of that player's library.
{w}{u}{b}{r}{g}{t}: Target opponent reveals their hand. You may choose a nonland card from it and exile it. For as long as that card remains exiled you may cast it, and you may spend mana as though it were mana of any type to cast it.