Mikaeus, the Unhallowed, and Spawning Pit

Prerequisites

• Mikaeus, the Unhallowed on the battlefield
• Spawning Pit on the battlefield

Steps

1. Activate Spawning Pit by sacrificing the creature with persist
2. When that creature dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it
3. Resolve the Spawning Pit ability
4. Activate Spawning Pit by sacrificing the persist creature
5. When the persist creature dies, its undying ability triggers, returning it from your graveyard to the battlefield with a +1/+1 counter on it
6. Resolve the Spawning Pit ability
7. Repeat

Results

• Infinite charge counters on a permanent
• Infinite creature ETB
• Infinite creature LTB
• Infinite creature sacrifice triggers
• Infinite death triggers