Dorsal Glow

After charging up Dorsal Glow as a Bonus Action on your turn, as an action you can exhale a beam of concentrated energy.

Each creature in a 30-foot line (5 feet wide) must make a Dexterity saving throw (DC = 8 + Con modifier + Proficiency Bonus). A creature takes 2d12 radiant damage on a failed save, and half as much on a successful one. The damage increases to 3d12 at 5th level, 4d12 at 10th level, 5d12 at 15th level, and 8d12 at 20th level. You can use this a number of times equal to your Proficiency Bonus per long rest.