Mikaeus, the Unhallowed, Grim Poppet, and Yahenni, Undying Partisan

Prerequisites

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

Steps

1. Activate Yahenni by sacrificing Grim Poppet
2. When Grim Poppet dies, its undying ability triggers, returning it from your graveyard to the battlefield with a +1/+1 counter on it
3. This will be removed by its static ability, which will result in Grim Poppet having two -1/-1 counters instead
4. Resolve the Yahenni ability
5. Repeat

Results

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