Blasting Station + Grazing Kelpie + Hardened Academic

Blasting Station

Grazing Kelpie

Hardened Academic

How it works

1. Activate Blasting Station by tapping it and sacrificing Grazing Kelpie.
2. When Grazing Kelpie dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it.
3. Hardened Academic and Blasting Station trigger.
4. Resolve the Hardened Academic trigger, putting a +1/+1 counter on Grazing Kelpie.
5. Resolve the Blasting Station trigger, untapping it.
6. Resolve the Blasting Station ability from step 1.
7. Repeat.