Electro Trap

The four balls levitate in the air, creating a 15 ft cube at a point you choose within range. Ever creature within the cube must make a Dexterity saving throw. A target takes 2d6 lighting damage and is stunned till the end of your next turn on a failure, or half as much on a successful one. 

If a creature tries to move within the cube, it must make a Dexterity saving throw. On a failure, the creature take 1d6 lighting damage and movement is reduced to 0.