Errant, Street Artist + Reality Spasm + Galvanic Iteration

Prerequisites

You control at least two mana producing permanents, one of which can tap to produce at least {U}.

Steps

1. Cast Galvanic Iteration by paying {U}{R}, copying the next instant or sorcery spell you cast.
2. Cast Reality Spasm by paying at least {3}{U}{U}, targeting at least three permanents and choosing the untap mode.
3. Galvanic Iteration triggers, copying Reality Spasm, targeting at least three permanents.
4. Holding priority, activate at least two mana-producing permanents you control by tapping them, adding at least {1}{U}.
5. Activate Errant by paying {1}{U} and tapping it, copying the Reality Spasm copy, targeting Errant and at least two mana-producing permanents you control.
6. Resolve the copy of Reality Spasm from step 3, untapping Errant and at least two mana-producing permanents you control.
7. Repeat from step 4.