Metamorphosis Fanatic, Felidar Guardian, and Yahenni, Undying Partisan

Prerequisites

• Metamorphosis Fanatic on the battlefield
• Felidar Guardian in hand
• Yahenni, Undying Partisan on the battlefield
• You have enough mana to cast Felidar Guardian

Steps

1. Cast Felidar Guardian by paying its mana cost
2. When Felidar Guardian enters the battlefield, it triggers, targeting Metamorphosis Fanatic
3. Holding priority, activate Yahenni by sacrificing Felidar Guardian
4. Resolve the Felidar Guardian ability, blinking Metamorphosis Fanatic
5. When Metamorphosis Fanatic enters the battlefield, it triggers, returning Felidar Guardian from your graveyard to the battlefield
6. Repeat from step 2

Results

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