Szarel, Genesis Shepherd + Cauldron of Souls + Clock of Omens + Phantom Train

Szarel, Genesis Shepherd

Cauldron of Souls

Clock of Omens

Phantom Train

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 Phantom Train 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 Phantom Train 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 intricate loop transforms a quiet assembly of machinery and life into an engine of endless rebirth, centered around Cauldron of Souls and Clock of Omens to manipulate artifact creatures. By tapping your artifacts to untap the Cauldron, you constantly refresh the persist keyword on your creatures while keeping the machine running. When Phantom Train demands a sacrifice, the fallen creature triggers Szarel, Genesis Shepherd, whose growth-granting passive turns the resulting death into a mounting pile of +1/+1 counters. Because these counters cancel out the -1/+1 counters left by persist, the cycle can be repeated indefinitely to generate boundless triggers and power.