Szarel, Genesis Shepherd, Cauldron of Souls, Clock of Omens, and Shilgengar, Sire of Famine

Prerequisites

• Szarel, Genesis Shepherd on the battlefield
• Cauldron of Souls on the battlefield
• Clock of Omens on the battlefield
• Shilgengar, Sire of Famine 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 Shilgengar 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 Shilgengar 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

Results

• Infinite LTB
• Infinite ETB
• Infinite sacrifice triggers
• Infinite death triggers
• Infinite Blood tokens
• Infinite mana artifacts you control can produce
• Infinite untap of artifacts you control