Magic Items

Weapon (warhammer), legendary (requires attunement)
Matalotok, the Frost Father, is an ancient hammer fashioned by Thrym, the god of frost giants. The favored weapon of the demon lord Kostchtchie, Matalotok is frigid to the touch and wreathed in mist.
You are immune to cold damage while holding Matalotok. Whenever it deals damage to a creature, the hammer radiates a burst of intense cold in a 30-foot-radius sphere. Each creature in that area takes 10 (3d6) cold damage.

Weapon (rapier), very rare (requires attunement)
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. This extraordinary weapon is crafted from a single piece of ice with a pommel wrapped in braided leaves. If wielded in temperatures in excess of 90 degrees, rivulets of water run down its blade—soaking the hand holding it. Despite this, it never melts away. This item can be found in the Dungeon Master’s Guide.