Tear to Oblivion

Your body becomes a bridge to the Elemental Planes as you draw a blade of pure lightning from your heart. When you cast this spell, you slice a 60-foot cone in front of you. Creatures in the cone must make a Dexterity saving throw. On a failed save, a creature takes 6d8 + 10 lightning damage, or half as much on a success.

For the duration of the spell, you gain advantage on Constitution saving throws to maintain concentration on this spell. Also, when you take the Attack action, you can forgo one attack to make a melee spell attack with the lightning blade. This blade has a range of 5 feet and uses your spellcasting modifier to hit. On a hit, the blade deals 4d8 + 10 lightning damage. The first time a creature takes damage from the lightning blade, they must make a Constitution saving throw. On a failed save, they are stunned until the start of your next turn. On a successful save, the attack has no other effects, and the creature cannot be stunned by the lightning blade for 24 hours.

You can also use your action to transform into lightning and attack all creatures in a 30-foot radius sphere. All creatures inside the sphere must make a Dexterity saving throw, taking 6d8 + 10 lightning damage on a failed save, and half that damage on a successful save. When this attack ends, you return to your previous position and form. 

When a creature is reduced to 0 hit points by any aspect of this spell, the creature and everything they are carrying, except magic items, are reduced to a pile of dark dust. The creature can only be returned to life by means of a true resurrection or wish spell.