Dragon Chain Lightning

A buildup of lightning forms in your palms and strikes out in a direction you choose. As it travels the front of the lightning begins to take on the form of a dragon.  It pierces the first target and then can shoot into another within 15ft.  You hit your casting modifier worth of creatures. (+2 means two extra creatures after the first target)  Any creature hit must make a Dexterity saving throw. A creature takes 8d12 lightning damage on a failed save, or half as much damage on a successful one. 
The lightning ignites flammable objects in the area that aren't being worn or carried.

At Higher Levels. When you cast this spell using a spell slot of 6th level or higher, the damage increases by 1d12 for each slot level above 5th.