Thor's Day: Laevateinn for D&D 5th Edition

LAEVATEINN
Magic staff, artifact (requires attunement by a spell caster)

Your spell save DC and spell attack bonus each increase by 3.

In addition, while attuned to the weapon you may utter a command word and transform Laevateinn into a a longsword as a bonus action.  You gain +3 to attack and damage rolls with this magic longsword. 

"Lævatein is there, that Loki with runes once made by the doors of death; In Lægjarn's chest by Sinmora lies it, and nine locks fasten it firm."