Trapjaw Kelpie + Yahenni, Undying Partisan + Hardened Academic

Trapjaw Kelpie

Yahenni, Undying Partisan

Hardened Academic

How it works

1. Activate Yahenni by sacrificing Trapjaw Kelpie.
2. When Trapjaw Kelpie 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 Trapjaw Kelpie.
4. Resolve the Yahenni ability.
5. Repeat.