Otherworldly Escort + Amoeboid Changeling + Thornbite Staff + Umbral Collar Zealot

Otherworldly Escort

Amoeboid Changeling

Thornbite Staff

Umbral Collar Zealot

How it works

1. Activate Amoeboid Changeling's second ability by tapping it, causing Otherworldly Escort to lose all creature types until end of turn.
2. Activate Umbral Collar Zealot by sacrificing Otherworldly Escort.
3. When Otherworldly Escort dies, it and Amoeboid Changeling trigger.
4. Resolve the Amoeboid Changeling trigger, untapping it.
5. Resolve the Otherworldly Escort trigger, returning itself from your graveyard to the battlefield as a Spirit Detective.
6. Resolve the Umbral Collar Zealot ability.
7. Repeat.

This looping mechanism hinges on stripping away creature types so that Otherworldly Escort keeps triggering its own resurrection clause every time it hits the graveyard. By using Amoeboid Changeling to make Otherworldly Escort lose all creature types, you bypass its safeguard against returning if it's a Spirit, allowing it to successfully recur itself whenever Umbral Collar Zealot sacrifices it. Meanwhile, Thornbite Staff and other synergy pieces can easily be integrated into this loop to capitalize on the endless cycle of death and rebirth.