Zellix, Sanity Flayer + Haunted One + Pith Driller + Phyrexian Altar + Intruder Alarm

Zellix, Sanity Flayer

Haunted One

Pith Driller

Phyrexian Altar

Intruder Alarm

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 Phyrexian Altar by sacrificing Pith Driller, adding 1.
6. When Pith Driller dies, its undying ability triggers, returning it from your graveyard to the battlefield with a +1/+1 counter on it.
7. When Pith Driller enters the battlefield, it and Intruder Alarm trigger.
8. Resolve the Pith Driller trigger, putting a -1/-1 counter on it.
9. Resolve the Intruder Alarm trigger, untapping all creatures.
10. Repeat.

This clever loop turns the milling engine of Zellix, Sanity Flayer into a self-sustaining mana and token factory, guided by the tribal buffs of Haunted One to grant your Horrors undying. By sacrificing Pith Driller to Phyrexian Altar, you generate the mana needed to activate Zellix's mill ability while feeding the sacrifice requirements. Whenever Pith Driller returns via undying, its entry triggers Intruder Alarm to untap your entire board, allowing Zellix to keep tapping and Pith Driller to safely neutralize its own +1/+1 counters using its -1/-1 counter ability.