Mikaeus, the Unhallowed + Gravelgill Axeshark + Phantom Train

Mikaeus, the Unhallowed

Gravelgill Axeshark

Phantom Train

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. Resolve the Phantom Train ability.
4. Activate Phantom Train by sacrificing Gravelgill Axeshark.
5. When Gravelgill Axeshark dies, its undying ability triggers, returning it from your graveyard to the battlefield with a +1/+1 counter on it.
6. Resolve the Phantom Train ability.
7. Repeat.

This clever loop thrives on the mathematical cancellation of opposing counters, turning Gravelgill Axeshark into an endlessly recycled sacrifice fodder for Phantom Train. Because Mikaeus, the Unhallowed grants undying to non-Human creatures while the Axeshark naturally possesses persist, sending the Axeshark to the graveyard alternately adds a +1/+1 counter and a -1/-1 counter—allowing these two triggered abilities to cleanly cancel each other out over and over. With Phantom Train happily converting each sacrifice into scaling +1/+1 counters for itself, you get an infinite engine of death triggers, enters-the-battlefield effects, and sacrifices.