Rally of Wings in exile (Rally of Wings exiled by Isochron Scepter).
Isochron Scepter and The Blackstaff of Waterdeep on the battlefield.
Creatures you control can tap to produce at least ({3} magic symbol) .
({U} magic symbol) available.
Steps
Activate all mana-producing creatures you control by tapping them, adding at least ({3} magic symbol) .
Activate The Blackstaff of Waterdeep by paying ({1} magic symbol) ({U} magic symbol) and tapping it, causing Isochron Scepter to become a 4/4 artifact creature.
Activate Isochron Scepter by paying ({2} magic symbol) and tapping it, casting a copy of Rally of Wings without paying its mana cost.
Resolve Rally of Wings, untapping all creatures you control.
Activate all mana-producing creatures you control by tapping them, adding at least ({3} magic symbol) .