The blade of this weapon is made of Eternal Ice and Infernal Steel and when the touched it is cold on one side but slightly warm on the other. The wielder of this blade is immune to the effects of extreme cold and heat(as descripted in the 5e DMG pp. When you hit with this weapon, you deal an extra 1d8 fire and 1d8 cold damage.

D-mannose

Weapon (any sword), legendary (requires attunement)

The blade of this weapon is made of Eternal Ice and Infernal Steel and when the touched it is cold on one side but slightly warm on the other. The wielder of this blade is immune to the effects of extreme cold and heat(as descripted in the 5e DMG pp. 110). When you hit with this weapon, you deal an extra 1d8 fire and 1d8 cold damage.

D. B. Sweeney

As an action, you can thrust the blade into the ground and cause a wall of blue fire and red ice to erupt from the ground as per the wall of ice spell (panels are not vulnerable to fire damage). Creatures take both fire and cold damage from this spell. The blade regains use of this effect at dawn.