Mikaeus, the Unhallowed + Umbral Collar Zealot + Persistent Constrictor

Mikaeus, the Unhallowed

Umbral Collar Zealot

Persistent Constrictor

How it works

1. Activate Umbral Collar Zealot by sacrificing Persistent Constrictor.
2. When Persistent Constrictor 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 Persistent Constrictor.
5. When Persistent Constrictor 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.