Frost Brand Weapon

Frost Brand generic variant, major tier, very rare (requires attunement)
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When you hit with an attack using this magic sword, the target takes an extra 1d6 cold damage. In addition, while you hold the sword, you have resistance to fire damage.
In freezing temperatures, the blade sheds bright light in a 10-foot radius and dim light for an additional 10 feet.
When you draw this weapon, you can extinguish all nonmagical flames within 30 feet of you. This property can be used no more than once per hour.
Base items. This item variant can be applied to the following base items:
Double-Bladed Scimitar (Frost Brand Double-Bladed Scimitar) Greatsword (Frost Brand Greatsword) Longsword (Frost Brand Longsword) Rapier (Frost Brand Rapier) Scimitar (Frost Brand Scimitar) Shortsword (Frost Brand Shortsword) Found On: Magic Item Table H
Frost Brand Shortsword DMG p171 Weapon, very rare (requires attunement) Major tier Martial weapon, melee weapon 2 lb. 1d6 piercing - finesse, light
When you hit with an attack using this magic sword, the target takes an extra 1d6 cold damage. In addition, while you hold the sword, you have resistance to fire damage.
In freezing temperatures, the blade sheds bright light in a 10-foot radius and dim light for an additional 10 feet.
When you draw this weapon, you can extinguish all nonmagical flames within 30 feet of you. This property can be used no more than once per hour.
Finesse. When making an attack with a finesse weapon, you use your choice of your Strength or Dexterity modifier for the attack and damage rolls. You must use the same modifier for both rolls.
Light. A light weapon is small and easy to handle, making it ideal for use when fighting with two weapons.
Found On: Magic Item Table H Source: DMG, page 171. Available in the SRD.

The party found this on the dead body of a dwarf in tree north of Wide Berth, it was delivering a package but was killed by some displacer beasts.