Death Lightning

You gather up dark and vicious energy within you and expel it in the form of blue and purple lightning. On your command, providing you are holding no items, the aura of lightning around your hands arcs out and hits one target of your choice within range.  The target is then electrically charged with the lightning, causing them extreme pain, as it drains their life force. Make a ranged spell attack against the target. If the target is wearing or is made of metal, you have advantage on this attack. On a hit, the target takes 1d6 lightning damage and 1d6 necrotic damage, and they must make a constitution saving throw, falling prone and stunned on a failed save and falling prone but not stunned on a success. If you cast this spell on the same creature in two or more consecutive turns, the lightning damage increases by 1 for each consecutive turn.