What are the abilities of Urza, Powerstone Prodigy?
user
Vigilance\n{1}, {T}: Draw a card, then discard a card.\nWhenever you discard one or more artifact cards, create a tapped Powerstone token. This ability triggers only once each turn. (The token is an artifact with "{T}: Add {C}. This mana can't be spent to cast a nonartifact spell.")
assistant