Agatha's Soul Cauldron, Immaculate Magistrate, and Barrenton Medic

Prerequisites

• Agatha's Soul Cauldron on the battlefield
• Immaculate Magistrate on the battlefield
• Barrenton Medic in exile
• You control at least two Elves
• Immaculate Magistrate does not have summoning sickness

Steps

1. Activate Immaculate Magistrate by tapping it, putting a +1/+1 counter on it for each Elf you control
2. Activate Immaculate Magistrate using Barrenton Medic's second ability by putting a -1/-1 counter on it, untapping it
3. Repeat
4. Once you have infinite +1/+1 counters on Immaculate Magistrate, you may instead target any other creature, and you may also untap them infinitely using Barrenton Medic's second ability
5. You may also repeat this loop whenever damage would be dealt to you or a permanent you control, and then use Barrenton Medic's first ability to prevent the damage

Results

• Infinite +1/+1 counters
• Infinite mana creatures you control can produce
• Infinite untap of creatures you control
• Prevent all damage that would be dealt to permanents you control
• Prevent all damage that would be dealt to you