Roar of the Kha in exile (exiled by Isochron Scepter).
Isochron Scepter and Ensoul Artifact on the battlefield.
Ensoul Artifact attached to Isochron Scepter.
You control creatures that can tap to produce at least ({3} magic symbol) .
Steps
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 Roar of the Kha without paying its mana cost, untapping all creatures.