Stalwart Successor + Umbral Collar Zealot + River Kelpie

Stalwart Successor

Umbral Collar Zealot

River Kelpie

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. When River Kelpie enters, it and Stalwart Successor trigger.
4. Resolve the River Kelpie trigger, causing you to draw a card
5. Resolve the Stalwart Successor trigger, putting a +1/+1 counter on River Kelpie
6. Resolve the Umbral Collar Zealot ability.
7. Repeat.