Mikaeus, the Unhallowed + Umbral Collar Zealot + Trapjaw Kelpie

Mikaeus, the Unhallowed

Umbral Collar Zealot

Trapjaw Kelpie

How it works

1. Activate Umbral Collar Zealot by sacrificing Trapjaw Kelpie.
2. When Trapjaw Kelpie 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 Trapjaw Kelpie.
5. When Trapjaw Kelpie 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.