Toph, the First Metalbender + Toph, Hardheaded Teacher + Gruul Turf + Yahenni, Undying Partisan

Toph, the First Metalbender

Toph, Hardheaded Teacher

Gruul Turf

Yahenni, Undying Partisan

How it works

1. Cast the artifact by paying 0.
2. Toph, Hardheaded Teacher triggers, earthbending Gruul Turf.
3. Resolve the artifact spell.
4. Activate Yahenni by sacrificing Gruul Turf.
5. When Gruul Turf dies, Toph, Hardheaded Teach triggers, returning Gruul Turf from your graveyard to the battlefield tapped.
6. When Gruul Turf 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 Yahenni ability
8. Repeat.

This loop transforms free artifacts into an endless cascade of triggers by turning them into lands via Toph, the First Metalbender, allowing them to be repeatedly bounced back to your hand. When you cast your free artifact, Toph, Hardheaded Teacher triggers its earthbend ability on Gruul Turf, turning the bounce-land into a creature so Yahenni, Undying Partisan can sacrifice it to gain indestructible. As Gruul Turf dies, its own safety net and Toph, Hardheaded Teacher's persistence allow it to return to the battlefield tapped, instantly triggering its own entry ability to pick up the artifact you just cast and reset the whole engine.