Agatha's Soul Cauldron + Immaculate Magistrate + Barrenton Medic

Agatha's Soul Cauldron

Immaculate Magistrate

Barrenton Medic

How it works

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.

This brilliant engine relies on Agatha's Soul Cauldron to bridge the gap, granting Barrenton Medic's self-untapping ability directly to Immaculate Magistrate by exiling the Medic and dropping a +1/+1 counter onto the Magistrate. Once empowered, Immaculate Magistrate can tap to add a massive pile of +1/+1 counters to itself for every Elf you control, immediately neutralizing those counters using Barrenton Medic's ability to untap and repeat the process endlessly. This loop scales your creatures to staggering heights while generating infinite untaps, letting you redirect the growth to any creature you control and completely blanking incoming damage with the Medic's prevention shield.