Thran Vigil + Yahenni, Undying Partisan + Grazing Kelpie

Thran Vigil

Yahenni, Undying Partisan

Grazing Kelpie

How it works

1. Activate Yahenni 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 Yahenni ability.
5. Repeat.