Stalwart Successor + Umbral Collar Zealot + Grazing Kelpie

Stalwart Successor

Umbral Collar Zealot

Grazing Kelpie

How it works

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