Chillwind Strike

The weapon used in the spell’s casting is wreathed in icy frost, and you make a melee attack with it against one creature within 5 feet of you. The attack uses your spellcasting ability for the attack and damage rolls instead of using Strength or Dexterity. If the attack deals damage, it can be Cold damage or the weapon’s normal damage type (your choice) and the damaged creature's Speed is reduced by 10 feet until the start of your next turn..

Cantrip Upgrade. Whether you deal Cold damage or the weapon’s normal damage type, the attack deals extra Cold damage when you reach levels 5 (1d6), 11 (2d6), and 17 (3d6).