Vigor + Walking Ballista + Quest for Pure Flame

Vigor

Walking Ballista

Quest for Pure Flame

How it works

1. Activate Quest for Pure Flame by removing four quest counters from it and sacrificing it, doubling the amount of damage sources you control deal this turn.
2. Activate Walking Ballista's second ability by removing a +1/+1 counter from it, putting two +1/+1 counters on it due to Vigor.
3. Activate Walking Ballista's second ability by removing a +1/+1 counter from it, dealing 2 damage to any target.
4. Repeat from step 2 as desired.