Rat King, Verminister + Intruder Alarm + Belonging + Phantom Train

Rat King, Verminister

Intruder Alarm

Belonging

Phantom Train

How it works

1. Cast Belonging by paying 5.
2. When Belonging enters, it and Intruder Alarm trigger.
3. Resolve the Belonging trigger, creating three 1/1 Shapeshifter creature tokens with changeling.
4. When the Shapeshifters enter, Intruder Alarm triggers three times. Resolve the Intruder Alarm triggers from this step and step 2, untapping all creatures four times.
5. Activate Phantom Train by sacrificing Belonging.
6. Activate Rat King by tapping it and sacrificing the Shapeshifters, returning Belonging from your graveyard to the battlefield.
7. Repeat from step 2.

This clever loop relies on Intruder Alarm to turn every creature entry into an untap catalyst, allowing Rat King, Verminister to repeatedly sacrifice and recur your board. When you cast Belonging, its entry triggers the Alarm alongside its own ability to flood the board with changelings, providing the fodder needed to fuel Rat King's revival ability. Meanwhile, Phantom Train acts as a convenient sacrifice outlet to send Belonging back to the graveyard just in time, while also happily soaking up the infinite +1/+1 counters generated along the way.