Mastery of the Unseen

If a double-faced card is manifested, it will be put onto the battlefield face down. While face down, it can't transform. If the front face of the card is a creature card, you can turn it face up by paying its mana cost. If you do, its front face will be up.

There are no cards in the Fate Reforged set that would turn a face-down instant or sorcery card on the battlefield face up, but some older cards can try to do this. If something tries to turn a face-down instant or sorcery card on the battlefield face up, reveal that card to show all players it's an instant or sorcery card. The permanent remains on the battlefield face down. Abilities that trigger when a permanent turns face up won't trigger, because even though you revealed the card, it never turned face up.

At any time, you can look at a face-down permanent you control. You can't look at face-down permanents you don't control unless an effect allows you to or instructs you to.