Mikaeus, the Unhallowed, and Yahenni, Undying Partisan

Prerequisites

• Mikaeus, the Unhallowed on the battlefield
• Yahenni, Undying Partisan on the battlefield

Steps

1. Activate Yahenni by sacrificing the persist creature
2. When the persist creature dies, its persist ability triggers if it didn't have a -1/-1 counter on it, and its undying ability triggers if it didn't have a +1/+1 counter on it
3. Resolve the persist trigger, if applicable, returning the creature from your graveyard to the battlefield with a -1/-1 counter on it
4. Resolve the undying trigger, if applicable, returning the creature from your graveyard to the battlefield with a +1/+1 counter on it
5. Resolve the Yahenni ability
6. Repeat

Results

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