System Shock

You unleash a crackling pulse of elemental energy toward a single creature within range, fusing lightning precision with a core of biting cold. This spell's energy travels in a straight line up to 100 feet.  Make a ranged spell attack against the target. On a hit, the target takes 4d6 cold damage, and you attempt to disrupt their internal rhythms with a chilling overload.

If the target is damaged, their speed is halved, they can't take reactions, and on their turn they can either take an action or a bonus action, not both.

The duration of the slow effect depends on how much cold damage the target takes:

4-10 damage: Slowed for 0 rounds

11-17 damage: Slowed for 1 round

18-24 damage: Slowed for 2 rounds 

24+ damage: Slowed for 3 rounds

At Higher Levels. When you cast this spell using a spell slot of 4th level or higher, increase the cold damage by 1d6 for each slot level above 3rd.