Vargas, the Nightwolf

When Vargas the Nightwolf damages an
opponent look at the top six cards of
that opponent's library, exile one of them, then put the rest on the bottom of that library in a random order.
You may cast that card for as long as it remains exiled.
At the start of any upkeep if no spells were cast last turn, transform Vargas the Nightwolf.