Coldsnap

Weapon (whip), rare (requires attunement)

This icy whip deals an extra 1d4 cold damage to any target it hits. In addition, you have a +1 bonus to attack and damage rolls made with this magic weapon.

The whip has 3 charges and regains all of them each day at dawn. When you hit a creature that is not immune to cold damage with this weapon, you can expend 1 of its charges to force the creature to make a DC 15 Constitution saving throw. On a failure, its speed becomes 0 until the start of your next turn. On a success, its speed is halved instead. 

Once you attune to this weapon, its normally frigid handle feels warm to the touch.