Umbral Collar Zealot + Thran Vigil + Grazing Kelpie

Umbral Collar Zealot

Thran Vigil

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. Thran Vigil triggers, putting a +1/+1 counter on Grazing Kelpie.
4. Resolve the Umbral Collar Zealot ability.
5. Repeat.