Blasting Station + Lingering Tormentor + Hardened Academic

Blasting Station

Lingering Tormentor

Hardened Academic

How it works

1. Activate Blasting Station by tapping it and sacrificing Lingering Tormentor.
2. When Lingering Tormentor 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 Lingering Tormentor.
5. Resolve the Blasting Station trigger, untapping it.
6. Resolve the Blasting Station ability from step 1.
7. Repeat.