Arc Lightning

Your hands begin to spark with electric energy that you guide towards a target in range. The target must succeed on a Dexterity Saving Throw. The creature takes 4d8 lighning damage or half as much on a successful save. 

Lightning arcs from this creature and you can target two additional creatures, within 20 ft., in this way. Each creature must make a new Dexterity Saving Throw. These creatures take 2d8 lightning damage on a failed save, or half as much on a successful one.

At Higher Levels:

When you cast this spell using a slot of 5th level or higher, the damage (both initial and arcs) increases by 1d8, and an extra arc leaps from the first target to another, for each slot above 4th level.