Xavier Sal, Infested Captain + Agatha's Soul Cauldron + Barrenton Medic + Saproling Burst

Xavier Sal, Infested Captain

Agatha's Soul Cauldron

Barrenton Medic

Saproling Burst

How it works

1. Activate Xavier Sal's second ability by tapping it and sacrificing another creature, putting a +1/+1 counter on it and a fade counter on Saproling Burst.
2. Activate Saproling Burst by removing a fade counter from it, creating a Saproling creature token.
3. Activate Xavier Sal using Barrenton Medic's second ability by putting a -1/-1 counter on it, untapping Xavier Sal.
4. Repeat.

This loop hinges on Agatha's Soul Cauldron granting Barrenton Medic's untap ability to Xavier Sal, Infested Captain, allowing him to endlessly untap himself by placing -1/-1 counters on his own head. With Xavier Sal's activated abilities constantly cycling, you can sacrifice creatures to fuel his proliferate ability while managing the counters on Saproling Burst. The Burst steps in to continuously generate Saproling tokens that act as sacrificial fodder, whose power and toughness naturally fluctuate with the fading counters.