Mikaeus, the Unhallowed + Otherworldly Escort + Phantom Train

Mikaeus, the Unhallowed

Otherworldly Escort

Phantom Train

How it works

1. Activate Phantom Train by sacrificing Otherworldly Escort.
2. When Otherworldly Escort dies, it triggers, returning itself from your graveyard to the battlefield as a Spirit Detective.
3. Resolve the Phantom Train ability.
4. Activate Phantom Train by sacrificing Otherworldly Escort.
5. When Otherworldly Escort 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 loop relies on an ingenious interplay between sacrifice outlets and resurrection mechanics to continually cycle Otherworldly Escort back and forth from the battlefield. You begin by feeding the Escort to Phantom Train, which triggers its own replacement clause to return it to play as a Spirit. Because it is no longer a human, the static lord effect from Mikaeus, the Unhallowed grants it undying, ensuring that the next time Phantom Train sacrifices it, undying brings it right back with a +1/+1 counter instead. By alternating between these two distinct return methods, the engine loops indefinitely to generate an endless stream of sacrifice, death, and entry triggers.