Phyrexian Altar + Dualcaster Mage + Extract from Darkness

Phyrexian Altar

Dualcaster Mage

Extract from Darkness

How it works

1. Cast Extract from Darkness by paying its mana cost
2. Holding priority, cast Dualcaster Mage by paying its mana cost.
3. When Dualcaster Mage enters, it triggers, targeting Extract from Darkness.
4. Holding priority, activate Phyrexian Altar by sacrificing Dualcaster Mage.
5. Resolve the Dualcaster Mage trigger, copying Extract from Darkness
6. Resolve the Extract from Darkness copy, causing each player to mill two cards and returning Dualcaster Mage from your graveyard to the battlefield.
7. Repeat from step 3.

This looping marvel sets up a closed-loop engine using Extract from Darkness to continually pull resources right back out of the graveyard. When you cast Dualcaster Mage, its entry trigger targets the original spell, copying it while leaving the primary copy to resolve and bring the Mage straight back to the battlefield. Meanwhile, sacrificing that same Dualcaster Mage to Phyrexian Altar immediately converts it into a steady stream of colored mana to fund the next iteration.