The sword of duck AKA Clarent is one of three created by the Thunder-Ducks. Although, nobody knows what these ducks actually are, most inscriptions show images of a duck wielding lightning. After the incident with Typhon it is possible that Insert Name Here was the creator of the sword as a weapon designed to defeat the Doppelgänger. Granted, that was a story during the corruption to the timeline, so it is debatable. Some even claim the sword never was the same in any timeline and Insert Name Here merely made a twin sword, which would in fact make his sword Clarent, and Lawsome1997's Excalibur. Either way, it has ancient magical origins. After it's discovery it was claimed by Lawsome1997 and wielded by him until Cantavanda (Death) claimed it when Lawsome1997 was assimilated by The Game. It is unknown whether that version was lost when Death was exorcized from the universe; however, it is irrelevant since time was reset and the future changed.
The sword is several times its weight to anyone other than the one wielding it. As a result it can deal extremely strong blows.
See The Trident of Duck and The Dagger of Duck for other weapons.