Yahenni, Undying Partisan + Faceless Butcher + Metamorphosis Fanatic

Yahenni, Undying Partisan

Faceless Butcher

Metamorphosis Fanatic

How it works

1. Cast Faceless Butcher by paying its mana cost.
2. When Faceless Butcher enters, its first ability triggers, exiling Metamorphosis Fanatic.
3. Activate Yahenni by sacrificing Faceless Butcher.
4. When Faceless Butcher dies, its second ability triggers, returning Metamorphosis Fanatic from exile to the battlefield.
5. When Metamorphosis Fanatic enters, it triggers, returning Faceless Butcher from your graveyard to the battlefield.
6. When Faceless Butcher enters, its first ability triggers, exiling Metamorphosis Fanatic.
7. Resolve the Yahenni ability.
8. Repeat from step 3.

This infinite loop relies on a clever recursion cycle between Faceless Butcher and Metamorphosis Fanatic, where each creature entering the battlefield immediately pulls the other back from exile or the graveyard. Meanwhile, Yahenni, Undying Partisan serves as the willing executioner to kick off the loop by sacrificing the Butcher, all while growing larger with each iteration thanks to its own death-triggered growth.