Chilling Smite

The next time you hit a creature with a melee weapon attack during the spell’s duration, your weapon freeze over and starts spewing an icy mist and the attack deals an extra 1d4 cold damage to the target and reduces the target's speed by half until the spell ends. The target accumulates a chill counter. 

At the start of each of its turns until the spell ends, the target must make a Constitution saving throw. On a failed save, it takes 1d4 cold damage for each chill counter it has, accumulates an additional chill counter and is restrained. On a successful save, the spell ends.

Being chilled makes saving increasingly more difficult. Each chill counter a target has increases the saving throw difficulty by one. Chill counters max out at 6. 

At Higher Levels. When you cast this spell using a spell slot of 2nd level or higher, the initial extra damage dealt by the attack increases by 1d6 for each slot.