Mikaeus, the Unhallowed + Rendclaw Trow + Phantom Train

Mikaeus, the Unhallowed

Rendclaw Trow

Phantom Train

How it works

1. Activate Phantom Train by sacrificing Rendclaw Trow.
2. When Rendclaw Trow 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 Rendclaw Trow.
5. When Rendclaw Trow 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 relies on the opposing counter mechanics of undying and persist to endlessly recycle a single creature through the graveyard. When you feed Rendclaw Trow to Phantom Train's sacrifice ability, its persist trigger brings it back with a -1/-1 counter, but Mikaeus, the Unhallowed provides a crucial static buff that grants the Trow undying as well; because the -1/-1 and +1/+1 counters elegantly cancel each other out upon entering, the Trow can alternate between returning via persist and undying with each subsequent sacrifice. This perpetual motion engine not only pumps infinite power into Phantom Train by letting you repeatedly add +1/+1 counters to it, but it also generates an endless stream of sacrifice, enter-the-battlefield, and death triggers.