2022-10-14 : 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.

2022-10-14 : If the card you exiled with the first ability is an instant, you may play it during your end step after Visions of Phyrexia's last ability has already resolved and created a Powerstone token. We call this having your cake and compleating it too.

2022-10-14 : If you played a card from exile for any reason, the ability won't trigger, even if it wasn't the card you exiled with the first ability.

2022-10-14 : Powerstone tokens are a kind of predefined token. Each one has the artifact subtype "Powerstone" and the ability "{T}: Add {C}. This mana can't be spent to cast a nonartifact spell."

2022-10-14 : You can use the {C} 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.

2022-10-14 : You must follow all normal timing rules for a card you play using Visions of Phyrexia's first ability and, if it's a spell, you must pay its costs to cast it.