Mikaeus, the Unhallowed + Altar of Dementia + Gravelgill Axeshark

Mikaeus, the Unhallowed

Altar of Dementia

Gravelgill Axeshark

How it works

1. Activate Altar of Dementia by sacrificing Gravelgill Axeshark.
2. When Gravelgill Axeshark 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 Gravelgill Axeshark.
5. When Gravelgill Axeshark 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.