Boethius's Blast

You direct a burst of lightning arcing arcing out from your extended arm. Make a ranged spell attack against the target. On a hit, the target takes 1d8 lightning damage. For each 8  rolled on the damage dice the arc of lightning hits an additional target within 30 ft of the original target

This spell's damage increases by 1d8 when you reach 5th level (2d8), 11th level (3d8), and 17th level (4d8).