Zellix, Sanity Flayer + Haunted One + Pith Driller + Ashnod's Altar + Faces of the Past

Zellix, Sanity Flayer

Haunted One

Pith Driller

Ashnod's Altar

Faces of the Past

How it works

1. Activate Zellix by paying 1 and tapping it.
2. Haunted One triggers, causing all Horrors you control to get +2/+0 and undying until end of turn.
3. Resolve the Zellix ability, causing a player to mill three cards.
4. If the player milled a creature card this way, Zellix triggers, creating a 1/1 Horror creature token.
5. Activate Ashnod's Altar by sacrificing Pith Driller, adding CC.
6. When Pith Driller dies, its undying ability and Faces of the Past trigger.
7. Resolve the Pith Driller trigger, returning it from your graveyard to the battlefield with a +1/+1 counter on it.
8. When Pith Driller enters the battlefield, it triggers, putting a -1/-1 counter on it.
9. Resolve the Faces of the Past trigger, untapping all Horrors.
10. Repeat.

This intricate loop begins by putting Haunted One in the command zone to grant your commanders undying whenever they become tapped, setting the stage for Zellix, Sanity Flayer to tap itself to mill cards and trigger creature token creation. By feeding these Horrors and Pith Driller into Ashnod's Altar for colorless mana, you fuel the entire engine while triggering Faces of the Past to untap your Horrors each time a creature dies. The true genius of the combo lies in Pith Driller, whose phyrexian mana cost allows it to enter the battlefield and immediately cancel out its own undying-granted +1/+1 counter with a -1/-1 counter, resetting its death loop infinitely.