Urza, Powerstone Prodigy
Legendary Creature — Human Artificer
Vigilance {1}, {T}: Draw a card, then discard a card. Whenever 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.")