Voltaic Sentinel

You manifest a 1-foot-diameter sphere of polarized electricity that hovers above the ground in an unoccupied space of your choice within range and lasts for the duration. The voltaic sentinel hurls bolts of electricity at nearby foes. The Sentinel is not alive and cannot be targeted or attacked by enemies. 

Any creatures of your choice that end their turn within 15 feet of the sentinel must make a Dexterity saving throw. The creature takes 2d6 lightning damage on a failed save, or half as much damage on a successful one.

The sentinel is immobile while you are within 10 feet of it. If you move more than 10 feet away from it, the sentinel follows you so that it remains within 10 feet of you. 

At Higher Levels. When you cast this spell using a spell slot of 3rd level or higher, the damage increases by 1d6 for each slot level above 2nd.