Mikaeus, the Unhallowed + Bloodied Ghost + Thermopod

Mikaeus, the Unhallowed

Bloodied Ghost

Thermopod

How it works

1. Activate Thermopod 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. Repeat.