Eirdu, Carrier of Dawn // Isilu, Carrier of Twilight + Howlgeist + Yahenni, Undying Partisan

Eirdu, Carrier of Dawn // Isilu, Carrier of Twilight

Howlgeist

Yahenni, Undying Partisan

How it works

1. Activate Yahenni by sacrificing Howlgeist
2. When Howlgeist dies, its undying ability triggers, returning it from your graveyard to the battlefield with a +1/+1 counter on it.
3. Activate Yahenni by sacrificing Howlgeist
4. When Howlgeist dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it.
5. Resolve both Yahenni abilities from step 1 and 3.
6. Repeat.