Technomancer + Phyrexian Altar + Auton Soldier

Technomancer

Phyrexian Altar

Auton Soldier

How it works

1. Cast Technomancer by paying 5.
2. When Technomancer enters, it triggers, causing you to mill three cards and return Auton Soldier from your graveyard to the battlefield as a copy of Technomancer.
3. When Auton Soldier enters, it triggers. Holding priority, activate Phyrexian Altar by sacrificing Auton Soldier.
4. Resolve the Auton Soldier trigger, causing you to mill three cards and return Auton Soldier from your graveyard to the battlefield as a copy of Technomancer.
5. Repeat from step 3.

This loop relies on an infinite recursion of entering and leaving the battlefield, anchored by Technomancer's ability to pull small artifact creatures out of the graveyard. By having Auton Soldier enter as a copy of Technomancer, it triggers its own graveyard retrieval—allowing you to sacrifice it to Phyrexian Altar for mana in response to its own ETB trigger. Because the copied Technomancer brings back Auton Soldier every single time, you can continuously churn through your graveyard, sacrifice the clones for any color of mana, and mill your entire deck in the process.