Szarel, Genesis Shepherd + Cauldron of Souls + Clock of Omens + Altar of Dementia

Szarel, Genesis Shepherd

Cauldron of Souls

Clock of Omens

Altar of Dementia

How it works

1. Activate Cauldron of Souls by tapping it, giving two nontoken artifact creatures persist until end of turn.
2. Activate Clock of Omens by tapping the nontoken artifact creatures, untapping Cauldron of Souls.
3. Activate Altar of Dementia by sacrificing one of the nontoken artifact creatures that doesn't have a -1/-1 counter on it.
4. When the creature dies, its persist ability and Szarel triggers.
5. Resolve the persist trigger, returning the creature from your graveyard to the battlefield.
6. Resolve the Szarel trigger, putting a number of +1/+1 counters on the other artifact creature.
7. Resolve the Altar of Dementia ability.
8. Repeat from step 3 once, instead sacrificing the creature who had counters placed on it in step 6.
9. Repeat from step 1.

This ingenious loop turns a pair of artifact creatures into an endless self-mill engine by leveraging their synergy across the battlefield and graveyard. You start by using Cauldron of Souls to grant persist to your two artifact creatures, which then feed Clock of Omens by tapping themselves to untap the Cauldron in a continuous gearwork cycle. When you sacrifice one of those creatures to Altar of Dementia to mill an opponent, it immediately returns thanks to persist, and Szarel, Genesis Shepherd steps in to place +1/+1 counters on the other creature. Because those newly added +1/+1 counters immediately cancel out the -1/-1 counters from persist, the creatures can continually cycle back and forth through the graveyard—a process further supported by Szarel, Genesis Shepherd allowing you to play lands from your graveyard if needed.