Frostbite

Weapon (Longsword or Battleaxe), Rare (Optional Attunement)

Frostbite is a rugged and violent weapon, with an twisting, rough cedar wood handle and a cold serrated blade that is akin to frosted glass.

This weapon grants +1 to attack and damage rolls made with it. When you hit with an attack made with this weapon, the target takes an additional 1d4 cold damage.

Winter's Breath (Requires Attunement)
While attuned to Frostbite, its wielder can use their bonus action to activate Winter's Breath and enhance Frostbite's power, gaining the following abilities:

Winter's Breath can be activated a number of times equal to the wielder's proficiency bonus and recharges on a long rest.