Metamorphosis Fanatic, Body Double, and Yahenni, Undying Partisan

Prerequisites

• Metamorphosis Fanatic in hand
• Body Double in the graveyard
• Yahenni, Undying Partisan on the battlefield

Steps

1. Cast Metamorphosis Fanatic by paying
2. When Metamorphosis Fanatic enters the battlefield, it triggers, targeting Body Double
3. Holding priority, activate Yahenni by sacrificing Metamorphosis Fanatic
4. Resolve the Metamorphosis Fanatic ability, returning Body Double from your graveyard to the battlefield as a copy of Metamorphosis Fanatic
5. When Body Double enters the battlefield, it triggers, targeting Metamorphosis Fanatic
6. Holding priority, activate Yahenni by sacrificing Body Double
7. Resolve the Body Double ability, returning Metamorphosis Fanatic from your graveyard to the battlefield
8. Repeat from step 2

Results

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