Combustion

You choose three creatures you can see within your line of sight. You have to concentrate on this spell either until 1 minute has passed, or until you snap your fingers. When either of these happen, every chosen creature combust into a fiery explosion. Each creature in 20-foot-radius spheres centered on the chosen creatures must make a Dexterity saving throw. They take 6d6 fire damage on a failed save, or half as much damage on a successful one.

At Higher Levels. When you cast this spell using a spell slot of 6th level or higher, the damage increases by 1d6 for each slot level above 5th.