Stalwart Successor + River Kelpie + Yahenni, Undying Partisan

Stalwart Successor

River Kelpie

Yahenni, Undying Partisan

How it works

1. Activate Yahenni 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 Yahenni ability.
7. Repeat.