Visions of Phyrexia (Extended Art) [The Brothers' War]

At the beginning of your upkeep, exile the top card of your library. You may play that card this turn.

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 “T: Add C. This mana can't be spent to cast a nonartifact spell.”)