Szarel, Genesis Shepherd + Cauldron of Souls + Clock of Omens + Ashnod's Altar

Szarel, Genesis Shepherd

Cauldron of Souls

Clock of Omens

Ashnod's Altar

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 Ashnod's Altar 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. Repeat from step 3 once, instead sacrificing the creature who had counters placed on it in step 6.
8. Repeat from step 1.

This engine operates by locking two artifact creatures into an endless loop of sacrifice and resurrection, fueled by Ashnod's Altar to generate infinite colorless mana alongside endless death and entry triggers. Cauldron of Souls grants the necessary persist ability to those creatures, while Clock of Omens keeps the Cauldron active by tapping the creatures themselves. Meanwhile, Szarel, Genesis Shepherd turns every sacrifice into a scaling stat-boost by leveraging its power to place +1/+1 counters—which cleverly cancel out the -1/-1 counters from persist, ensuring the creatures can persist indefinitely and even allowing you to replay lands directly from your graveyard if needed.