Return target artifact, enchantment, or planeswalker card from your graveyard to the battlefield. Create a tapped Powerstone token. (It's an artifact with ": Add . This mana can't be spent to cast a nonartifact spell.")
"Throw the bodies out. They'll just weigh down the frame."
—Rolf, Argivian mechanic
(14/10/2022)
Powerstone tokens are a kind of predefined token. Each one has the artifact subtype "Powerstone" and the ability ": Add . This mana can't be spent to cast a nonartifact spell."
(14/10/2022)
You can use the added by a Powerstone token on anything that isn't a nonartifact spell. This includes paying costs to activate abilities of both artifact and nonartifact permanents, paying ward costs, and so on.
(14/10/2022)
Although all the cards in The Brothers' War that create Powerstone tokens create a tapped Powerstone token, entering the battlefield tapped isn't part of the token's definition. Notably, if you create a token that is a copy of a Powerstone token, the token copy won't enter the battlefield tapped.
