Mikaeus, the Unhallowed + Lingering Tormentor + Phantom Train

Mikaeus, the Unhallowed

Lingering Tormentor

Phantom Train

How it works

1. Activate Phantom Train by 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. Resolve the Phantom Train ability.
4. Activate Phantom Train by sacrificing Lingering Tormentor.
5. When Lingering Tormentor 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.