Mjalnar, known as the Sword of Balenight, was a great Frost Blade wielded by the Space Wolves Primarch Leman Russ. It is said that Mjalnar's teeth were torn from the maw of the Fenrisian Kraken Gormenjarl. The weapon is also said to be ancient, dating back to the Age of Strife. Mjalnar replaced Krakenmaw, the Frost Blade Russ had lost at the hands of Angron during the Night of the Wolf.
Mjalnar is likely a derivative of Mjolnir, the name of Thor's hammer from Norse mythology.