Eirdu, Carrier of Dawn // Isilu, Carrier of Twilight + Phantom Train + Witch-king, Sky Scourge

Eirdu, Carrier of Dawn // Isilu, Carrier of Twilight

Phantom Train

Witch-king, Sky Scourge

How it works

1. Activate Phantom Train by sacrificing Witch-king
2. When Witch-king dies, its undying ability triggers, returning it from your graveyard to the battlefield with a +1/+1 counter on it.
3. Activate Phantom Train by sacrificing Witch-king
4. When Witch-king dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it.
5. Resolve both Phantom Train abilities from step 1 and 3.
6. Repeat.

This loop relies on manipulating Witch-king, Sky Scourge's interaction with counters through Phantom Train's sacrifice ability. Because Eirdu, Carrier of Dawn // Isilu, Carrier of Twilight grants its persist ability to your other nontoken creatures while transformed, sending Witch-king, Sky Scourge to the graveyard alternates between triggering undying and persist as long as counters cancel each other out, all while Phantom Train steadily grows with infinite +1/+1 counters.