A-Visions of Phyrexia (BRO-A-156) - The Brothers' War

At the beginning of your upkeep, exile the top two cards of your library. Until your next end step, you may play one of those cards.
At the beginning of your end step, if you didn't play a card from exile this turn, create a tapped Powerstone token. (It's an artifact with ": Add . This mana can't be spent to cast a nonartifact spell.")