Arcing Zap

You create an electrical shock that jumps towards a creature of your choice that you can see within range. The shock may then continue to arc to other nearby enemies.

Make a ranged spell attack against a creature in range that you can see, on a hit you may choose to: 

Spend all available damage dice to deal lightning damage to one target.

or

Deal 1d4 lightning damage then have the spell arc to a new creature, that you can see within 10ft of the previous target. You may continue to target additional creatures in this way as long as they are visible to you and are each within 10ft of the most previous targeted creature. Each additional creature targeted this way must be a new target and cannot have been a target of the spell already on this turn. Each creature targeted after the first must make a Dexterity saving throw suffering 1d4 on a failed save, or half as much on a successful one. The number of additional creatures you may target is equal to the remaining unspent damage dice of this spell.

This spell's damage dice count increases by 1d4 when you reach 5th level (3d4), 11th level (4d4) and 17th level (5d4).