Danger Poof

Deathtouch
You looked away for one second: When Danger
enters the battlefield, look at the top four cards
of target opponent's library, exile one of them
face down, then put the rest on the bottom of
that library in any order. 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.
"Secrets, like steaks, are easy to steal."