Voltaic Lash

You create a long whip of flowing lightning and carry it in your hand.
The whip has a range of 15 feet. When you cast this spell and as an action on subsequent turns you may make a melee spell attack with the whip. You have advantage on the attack roll if the target is wearing armor made of metal. On a hit, it deals 4d8 lightning damage and the target must make a constitution saving throw. On a failed save, the target is stunned until the end of their next turn. On a success, they are not stunned.