Sven, Last Fatebreaker

Whenever you fateseal, put a +1/+1 counter
on Sven, Last Fatebreaker.
Whenever Sven, Last Fatebreaker attacks, fateseal X, where X is equal to its power.
(To fateseal x, look at the top x cards of an opponent's library, then put any number of them
on the bottom of that player's library and the rest
on top in any order.)