Umbral Collar Zealot + River Kelpie + Thran Vigil

Umbral Collar Zealot

River Kelpie

Thran Vigil

How it works

1. Activate Umbral Collar Zealot by sacrificing River Kelpie.
2. When River Kelpie dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it.
3. Thran Vigil and River Kelpie trigger.
4. Resolve the Thran Vigil trigger, putting a +1/+1 counter on River Kelpie.
5. Resolve the River Kelpie trigger, causing you to draw a card.
6. Resolve the Umbral Collar Zealot ability
7. Repeat.