Strength of Will + Walking Ballista + High Score

Steps

1. Cast Strength of Will by paying {1}{G}, targeting Walking Ballista.
2. Activate Walking Ballista by removing a +1/+1 counter from it, dealing 1 damage to it.
3. Walking Ballista triggers, putting two +1/+1 counters on it due to High Score.
4. Activate Walking Ballista by removing a +1/+1 counter from it, dealing 1 damage to any target.
5. Repeat from step 2.