Rally of Wings in exile (Rally of Wings exiled by Isochron Scepter).
Isochron Scepter on the battlefield.
Karn's Touch in hand.
You control creatures that can tap to produce at least ({3} magic symbol) .
({U} magic symbol) ({U} magic symbol) available.
Steps
Cast Karn's Touch by paying ({U} magic symbol) ({U} magic symbol) , targeting Isochron Scepter, causing it to become an artifact creature until end of turn.
Activate creatures you control by tapping those, adding ({3} magic symbol) .
Activate Isochron Scepter by paying ({2} magic symbol) and tapping it, casting a copy of Rally of Wings without paying its mana cost, untapping all creatures.