Blightning

A stroke of violet lightning forming a line 100 feet long and 5 feet wide blasts out from you in a direction you choose. Each creature in the line must make a Dexterity saving throw. A creature takes 4d6 lightning damage and 4d6 necrotic damage. on a failed save and lowers the target's AC-1., or 4d6 lightning damage on a successful one.

At Higher Levels. When you cast this spell using a spell slot of 4th level or higher, the damage increases by 1d6 lightning damage and lowers -1AC additionally for each slot level above 3rd