Mara Kiren, Mindbreaker

Eminence - Whenever one or more creatures you
own attack, if Mara Kiren, Mindbreaker is in your
command zone or on the battlefield, exile the top
card of each opponent's library.
Flying, lifelink, menace
At the beginning of each opponent's end step
you may pay {w}{u}{b}{r}, if you do, put a
creature that player owns from exile onto the
battlefield under your control.