Solarion, Agatha's Soul Cauldron, and Barrenton Medic

Prerequisites

• Solarion on the battlefield
• Agatha's Soul Cauldron on the battlefield
• Barrenton Medic in exile

Steps

1. Activate Solarion by tapping it, doubling the number of +1/+1 counters on it
2. Activate Solarion using Barrenton Medic's second ability by putting a -1/-1 counter on it, untapping Solarion
3. Repeat

Results

• Infinite +1/+1 counters on a creature