Mikaeus, the Unhallowed + Altar of Dementia + Twilight Shepherd

Mikaeus, the Unhallowed

Altar of Dementia

Twilight Shepherd

How it works

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