Toph, the First Metalbender + Toph, Hardheaded Teacher + Umbral Collar Zealot + Boros Garrison

Toph, the First Metalbender

Toph, Hardheaded Teacher

Umbral Collar Zealot

Boros Garrison

How it works

1. Cast the artifact by paying 0.
2. Toph, Hardheaded Teacher triggers, earthbending Boros Garrison.
3. Resolve the artifact spell.
4. Activate Umbral Collar Zealot by sacrificing Boros Garrison.
5. When Boros Garrison dies, Toph, Hardheaded Teach triggers, returning Boros Garrison from your graveyard to the battlefield tapped.
6. When Boros Garrison enters, it triggers, returning the artifact cast in step 1 from the battlefield to your hand, as it's a land due to Toph, the First Metalbender.
7. Resolve the Umbral Collar Zealot ability
8. Repeat.

This loop turns a zero-mana artifact into an infinite engine by leveraging a clever piece of type manipulation: Toph, the First Metalbender turns your nontoken artifacts into lands, which makes the artifact cast in step 1 valid prey for the bounce trigger of Boros Garrison when it enters the battlefield. Meanwhile, Toph, Hardheaded Teacher provides the earthbend triggers that animate your lands into creatures, allowing Umbral Collar Zealot to sacrifice Boros Garrison for a surveil and send it to the graveyard. Because Boros Garrison died as a land creature, Toph, Hardheaded Teacher's static or triggered return-to-battlefield effect (via its earthbend clause) brings it right back to repeat the cycle infinitely.