Strong, the Brutish Thespian, Agatha's Soul Cauldron, and Walking Ballista

Prerequisites

• Strong, the Brutish Thespian on the battlefield
• Agatha's Soul Cauldron on the battlefield
• Walking Ballista in exile
• Strong has at least one +1/+1 counter on it

Steps

1. Activate Strong using Walking Ballista's second ability by removing a +1/+1 counter from it, dealing 1 damage to Strong
2. Strong triggers, putting three +1/+1 counters on it and causing you to get three rad counters
3. Repeat an arbitrarily large number of times
4. Activate Strong using Walking Ballista's second ability by removing a +1/+1 counter from it, dealing 1 damage to any target
5. Repeat step 4 as desired

Results

• Infinite +1/+1 counters on Strong
• Infinite damage
• Infinite rad counters for yourself