Errant, Street Artist + Reality Spasm + Howl of the Horde

Errant, Street Artist

Reality Spasm

Howl of the Horde

How it works

1. Cast Howl of the Horde by paying 2, copying the next instant or sorcery spell you cast.
2. Cast Reality Spasm by paying at least 3, targeting at least three permanents and choosing the untap mode.
3. Howl of the Horde 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.
5. Activate Errant by paying 1 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.

This loop kicks off by setting the stage with Howl of the Horde, which ensures your next instant or sorcery spell gets copied. When you cast Reality Spasm with $X$ set to at least three, that setup grants you an initial copy, giving you multiple stacks on the stack to start the chain. By tapping your permanents for mana in response, you feed Errant, Street Artist's ability to copy those Reality Spasm copies on demand. As each copy resolves to untap Errant, Street Artist alongside your mana producers, you generate infinite mana and trigger any magecraft effects indefinitely!