Stalwart Successor + Umbral Collar Zealot + Lingering Tormentor

Stalwart Successor

Umbral Collar Zealot

Lingering Tormentor

How it works

1. Activate Umbral Collar Zealot by sacrificing Lingering Tormentor
2. When Lingering Tormentor dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it.
3. When Lingering Tormentor enters, Stalwart Successor triggers, putting a +1/+1 counter on Lingering Tormentor
4. Resolve the Umbral Collar Zealot ability.
5. Repeat.