Gravelgill Axeshark + Yahenni, Undying Partisan + Hardened Academic

Gravelgill Axeshark

Yahenni, Undying Partisan

Hardened Academic

How it works

1. Activate Yahenni by sacrificing Gravelgill Axeshark.
2. When Gravelgill Axeshark dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it.
3. Hardened Academic triggers, putting a +1/+1 counter on Gravelgill Axeshark.
4. Resolve the Yahenni ability.
5. Repeat.