Dawnsire, Sunstar Dreadnought + Vigor + Walking Ballista

Dawnsire, Sunstar Dreadnought

Vigor

Walking Ballista

How it works

1. Declare any creature as an attacker. Dawnsire triggers, attempting to deal 100 damage to Walking Ballista, but instead putting 100 +1/+1 counters on it due to Vigor.
2. Activate Walking Ballista 100 times by removing 100 +1/+1 counters from it, dealing 100 damage divided among any number of targets.