Mara, Kiren Mindbreaker

Flying, lifelink, menace
Eminence - At the beginning of your upkeep, if
Mara, Kiren Mindbreaker is in your command
zone or on the battlefield you may pay
{w}{u}{b}{r} if you do, put target creature an
opponent owns from exile onto the battlefield
under your control.
Whenever a creature you own attacks each player exiles the top card of their library.