Temporal Aperture

Oracle Text

5, T: Shuffle your library, then reveal the top card. Until end of turn, for as long as that card remains on top of your library, play with the top card of your library revealed and you may play that card without paying its mana cost. (If it has X in its mana cost, X is 0.)

Card Rulings

10/4/2004 While you do not have to pay the mana cost, you do have to pay any other costs described in the text that are paid when playing the card. If the cost in the card text is optional, such as with Buyback, you can optionally pay that cost.
10/4/2004 If your library is shuffled or that card otherwise leaves the top of your library, the effect ends.
10/4/2004 The card is removed from the top of the library when you play it, just like a card is removed from your hand when you play it.