Ball Lightning

A 5-foot-diameter sphere of electricity appears in an unoccupied space of your choice within range. The first time a creature moves within 10 feet of the sphere or starts its turn there, it must make a Dexterity saving throw as a bolt of lightning jumps from the sphere to strike it. On a failed save, the takes 3d6 lightning damage, and its speed is reduced to 0 until the start of its next turn. On a successful save, the target takes half damage, and its speed is not reduced.

Once the sphere has dealt this damage six times, or at the end of the duration, it disappears.

At Higher Levels. When you cast this spell using a spell slot of 4th level or higher, the sphere can deal damage two more times for each spell slot level above the 3rd.