Mikaeus, the Unhallowed, Soulstinger, and Yahenni, Undying Partisan

Prerequisites

• Mikaeus, the Unhallowed on the battlefield
• Soulstinger on the battlefield
• Yahenni, Undying Partisan on the battlefield
• Soulstinger does not have a +1/+1 counter on it

Steps

1. Activate Yahenni by sacrificing Soulstinger
2. When Soulstinger dies, its second and undying abilities trigger
3. Resolve the first trigger, allowing you to put a number of -1/-1 counters on a creature equal to the number that were on Soulstinger
4. Resolve the undying trigger, returning it from your graveyard to the battlefield with a +1/+1 counter on it
5. When Soulstinger enters the battlefield, its first ability triggers, putting two -1/-1 counters on it
6. Resolve the Yahenni ability, giving it indestructible until end of turn
7. Repeat

Results

• Infinite -1/-1 counters
• Infinite death triggers
• Infinite ETB
• Infinite LTB
• Infinite sacrifice triggers