Mikaeus, the Unhallowed + Bloodied Ghost + Altar of Dementia

Mikaeus, the Unhallowed

Bloodied Ghost

Altar of Dementia

How it works

1. Activate Altar of Dementia 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 Altar of Dementia ability.
4. Repeat.