Yahenni, Undying Partisan, Faceless Butcher, and Metamorphosis Fanatic

Prerequisites

• Yahenni, Undying Partisan on the battlefield
• Faceless Butcher in hand
• Metamorphosis Fanatic on the battlefield
• available

Steps

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

Results

• Infinite LTB
• Infinite ETB
• Infinite sacrifice triggers
• Infinite death triggers