Gravelgill Axeshark + Phantom Train + Hardened Academic

Gravelgill Axeshark

Phantom Train

Hardened Academic

How it works

1. Activate Phantom Train 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 Phantom Train ability.
5. Repeat.

This clever loop turns Gravelgill Axeshark into an endlessly recurring sacrifice engine by pairing its persist mechanic with Phantom Train's ability to devour creatures for fuel. Every time the Axeshark hits the graveyard, Hardened Academic's observant trigger notices a card leaving the graveyard and places a +1/+1 counter on a creature. That counter immediately neutralizes the -1/+1 counter the Axeshark would otherwise accumulate from persist, allowing the creature to return to the battlefield fresh and ready to be fed back into Phantom Train.