Mikaeus, the Unhallowed + Bloodied Ghost + Spawning Pit

Mikaeus, the Unhallowed

Bloodied Ghost

Spawning Pit

How it works

1. Activate Spawning Pit by sacrifiicing Bloodied Ghost.
2. When Bloodied Ghost dies, its undying ability triggers, returning it from your graveyard to the battlefield with a +1/+1 counter on it. When it enters, Bloodied Ghost will put a -1/-1 counter on itself, removing the +1/+1 counter.
3. Resolve the Spawning Pit ability.
4. Repeat.
5. Activate Spawning Pit by sacrificing Bloodied Ghost.
6. When Bloodied Ghost dies, its undying ability triggers, returning it from your graveyard to the battlefield without a +1/+1 counter on it due to its replacement effect.
7. Resolve the Spawning Pit ability
8. Repeat.