Reincarnation + Dualcaster Mage + Yahenni, Undying Partisan

Reincarnation

Dualcaster Mage

Yahenni, Undying Partisan

How it works

1. Cast Reincarnation by paying its mana cost.
2. Holding priority, cast Dualcaster Mage by paying its mana cost.
3. When Dualcaster Mage enters, it triggers, copying Reincarnation, with the copy targeting Dualcaster Mage.
4. Resolve the copy of Reincarnation.
5. Holding priority, activate Yahenni by sacrificing Dualcaster Mage.
6. When Dualcaster Mage dies, Reincarnation triggers, returning Dualcaster Mage from your graveyard to the battlefield.
7. Repeat from step 3.
8. Resolve all Yahenni abilities from step 5.

This brilliant recursive loop hinges on Dualcaster Mage copying Reincarnation to continually target itself upon entry, creating an endless cycle of rebirth. By sacrificing Dualcaster Mage to Yahenni, Undying Partisan's activated ability in response to the spell, you trigger Reincarnation's delayed effect to return the Mage right back to the battlefield—ready to copy the original spell once more. Meanwhile, Yahenni, Undying Partisan patiently reaps the benefits of all this mortality, growing infinitely large as the engine generates an endless stream of sacrifices and enter-the-battlefield triggers.