Conjure From Mist

Look at the top four cards of your library.
You may exile one of them face-down.
If you do, put it into your hand at the beginning of your next upkeep.
Put the rest of the cards on the bottom of your library in any order.
Every night, I see sleepers' dreams among the curling tendrils. Tonight, I have chosen one of them to become your waking nightmare.