Isaac Cheung, Mastermind

When Isaac Cheung, Mastermind enters the battlefield, exile all cards from all opponents' graveyards. You may cast those cards this turn,
and you may spend mana as though it were mana
of any type to cast those spells. At the beginning
of the next end step, if any of those cards remain exiled, return them to their owners' graveyards.
"Impossible? Well not with that attitude"