Mikaeus, the Unhallowed + Twilight Shepherd + Yahenni, Undying Partisan

Mikaeus, the Unhallowed

Twilight Shepherd

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. Resolve the Yahenni ability.
4. Activate Yahenni by sacrificing Twilight Shepherd.
5. When Twilight Shepherd dies, its undying ability triggers, returning it from your graveyard to the battlefield with a +1/+1 counter on it.
6. Resolve the Yahenni ability.
7. Repeat.