Twilight Shepherd + Thran Vigil + Yahenni, Undying Partisan

Twilight Shepherd

Thran Vigil

Yahenni, Undying Partisan

How it works

1. Activate Yahenni by sacrificing Twilight Shepherd.
2. When Twilight Shepherd 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 Twilight Shepherd.
4. Resolve the Yahenni ability.
5. Repeat.