Xavier Sal, Infested Captain + Agatha's Soul Cauldron + Scurry Oak + Barrenton Medic

Xavier Sal, Infested Captain

Agatha's Soul Cauldron

Scurry Oak

Barrenton Medic

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 Scurry Oak.
2. Scurry Oak triggers, creating a 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 engine relies on granting activated abilities through Agatha's Soul Cauldron to create an unstoppable loop of growth and token generation. By using Agatha's Soul Cauldron to exile Barrenton Medic and placing a +1/+1 counter on Xavier Sal, Infested Captain, Xavier gains Barrenton Medic's untap ability. You then use Xavier Sal's sacrifice ability to trigger Scurry Oak's evolution and token creation, while Barrenton Medic's self-counter ability untaps Xavier to repeat the sacrifice and generate infinite triggers.