Dominion Saboteur + Mikaeus, the Unhallowed + Umbral Collar Zealot

Dominion Saboteur

Mikaeus, the Unhallowed

Umbral Collar Zealot

How it works

1. Activate Umbral Collar Zealot by sacrificing Dominion Saboteur.
2. When Dominion Saboteur dies, its undying ability triggers, returning it from your graveyard to the battlefield with a +1/+1 counter on it. As it enters, choose to have it copy a non-Human you control with a -1/-1 counter on it, and then also enter with a -1/-1 counter on it.
3. Resolve the Umbral Collar Zealot ability
4. Repeat.