Pir, Imaginative Rascal, Vigor, and Walking Ballista

Prerequisites

• Pir, Imaginative Rascal on the battlefield
• Vigor on the battlefield
• Walking Ballista on the battlefield
• Walking Ballista has at least two +1/+1 counters on it

Steps

1. Activate Walking Ballista's second ability by removing a +1/+1 counter from it, putting two +1/+1 counters on it due to Vigor
2. Repeat an arbitrarily large number of times
3. Activate Walking Ballista's second ability by removing a +1/+1 counter from it, dealing 1 damage to any target
4. Repeat step 3 as many times as desired
5. You may also use step 3 to target another creature you control to put infinite +1/+1 counters on that creature

Results

• Infinite +1/+1 counters
• Infinite damage