Szarel, Genesis Shepherd, Cauldron of Souls, Clock of Omens, and Grinding Station

Prerequisites

• Szarel, Genesis Shepherd on the battlefield
• Cauldron of Souls on the battlefield
• Clock of Omens on the battlefield
• Grinding Station on the battlefield

Steps

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 Grinding Station by tapping it and 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. When the creature enters, Grinding Station triggers, untapping Grinding Station
7. Resolve the Szarel trigger, putting a number of +1/+1 counters on the other artifact creature
8. Resolve the Grinding Station ability from step 3
9. Repeat from step 3 once, instead sacrificing the creature who had counters placed on it in step 6
10. Repeat from step 1

Results

• Infinite LTB
• Infinite ETB
• Infinite sacrifice triggers
• Infinite death triggers
• Infinite mill
• Infinite self-mill