Mikaeus, the Unhallowed + Umbral Collar Zealot + Gravelgill Axeshark

Mikaeus, the Unhallowed

Umbral Collar Zealot

Gravelgill Axeshark

How it works

1. Activate Umbral Collar Zealot 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 Umbral Collar Zealot ability.
4. Activate Umbral Collar Zealot 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 Umbral Collar Zealot ability.
7. Repeat.