Mikaeus, the Unhallowed + Bloodied Ghost + Grimgrin, Corpse-Born

Mikaeus, the Unhallowed

Bloodied Ghost

Grimgrin, Corpse-Born

How it works

1. Activate Grimgrin 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 Grimgrin ability.
4. Repeat.
5. Activate Grimgrin 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 Grimgrin ability
8. Repeat.