Stalwart Successor + Umbral Collar Zealot + Kithkin Spellduster

Stalwart Successor

Umbral Collar Zealot

Kithkin Spellduster

How it works

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