When Urza enters, create a 0/0 colorless Construct artifact creature token with "This token gets +1/+1 for each artifact you control." Tap an untapped artifact you control: Add {U}. {5}: Shuffle your library, then exile the top card. Until end of turn, you may play that card without paying its mana cost.

(As this Saga enters and after your draw step, add a lore counter. Sacrifice after III.) I — This Saga gains "{T}: Add {C}." II — This Saga gains "{2}, {T}: Create a 0/0 colorless Construct artifact creature token with 'This token gets +1/+1 for each artifact you control.'" III — Search your library for an artifact card with mana cost {0} or {1}, put it onto the battlefield, then shuffle.

Flying {T}: Add one mana of any color.

Counter target spell. At the beginning of your next main phase, add an amount of {C} equal to that spell's mana value.