Szarel, Genesis Shepherd + Cauldron of Souls + Clock of Omens + Carrion Feeder

Szarel, Genesis Shepherd

Cauldron of Souls

Clock of Omens

Carrion Feeder

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 Carrion Feeder 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 Carrion Feeder 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 loop relies on cleverly juggling persist and counter manipulation to cycle your artifact creatures infinitely through the graveyard and battlefield. You start by using Cauldron of Souls to grant persist to your artifacts, and then tap them to power Clock of Omens so you can continually untap the Cauldron and keep the chain going. When you feed one of those creatures to Carrion Feeder, its death triggers Szarel, Genesis Shepherd, whose static-fueled trigger hands out +1/+1 counters to offset the -1/-1 counter from persist—allowing the creature to safely die and repeat the process over and over.