Toph, the First Metalbender + Toph, Hardheaded Teacher + Guildless Commons + Phantom Train

Toph, the First Metalbender

Toph, Hardheaded Teacher

Guildless Commons

Phantom Train

How it works

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

This loop turns the battlefield into an infinite engine by leveraging Toph, the First Metalbender's static ability to treat your nontoken artifacts as lands. With that foundation set, casting a zero-mana artifact triggers Toph, Hardheaded Teacher to animate Guildless Commons, which can then be fed to Phantom Train. Because Guildless Commons is recognized as a land, its death triggers Toph, Hardheaded Teacher's safety net to return it straight to the battlefield, where its own entry trigger bounces the original zero-mana artifact back to your hand to start the cycle anew.