Mikaeus, the Unhallowed + Defiant Greatmaw + Phantom Train

Mikaeus, the Unhallowed

Defiant Greatmaw

Phantom Train

How it works

1. Activate Phantom Train by sacrificing Defiant Greatmaw.
2. When Defiant Greatmaw dies, its undying ability triggers, returning it from your graveyard to the battlefield with a +1/+1 counter on it.
3. When Defiant Greatmaw enters the battlefield, its first ability triggers, putting two -1/-1 counters on it.
4. Defiant Greatmaw's second ability triggers, removing a -1/-1 counter from another creature you control.
5. Resolve the Phantom Train ability from step 1
6. Repeat.

This resilient loop relies on Mikaeus, the Unhallowed to grant undying to your non-Human creatures, turning the graveyard into a revolving door. By using Phantom Train to sacrifice Defiant Greatmaw, you trigger that undying ability to bring it right back to the battlefield with a +1/+1 counter. As Defiant Greatmaw enters, its triggered ability places two -1/-1 counters on itself, which immediately annihilates the existing +1/+1 counter through state-based actions and sets up an infinite engine of death and rebirth.