Frostbrand

Weapon Magical Rare (this item requires attunement)

You can use a bonus action to speak this magic sword's command word, causing freezing blue flames to erupt from the blade. Whilst the sword is ablaze, it deals an extra 2d6 cold damage to any target it hits. The flame lasts until you use a bonus action to speak the command word again, or until you sheath or drop the sword. In cold conditions, these flames shed bright light in a 10 foot radius and dim light for an additional 10 feet. Proficiency with a Longsword allows you to add your proficiency bonus to the attack roll for any attack you make with it.