Dusk Claymore

The was a magical Sword of light used by the Sage of Water in.

Design
The Sword appears to be a longsword, and the blade's length suggests that it may be a two-handed weapon. However, Ganondorf wields it both one- and two-handed, although this could be due to his great strength.

Twilight Princess
Hundreds of years before Twilight Princess, the Sage of Water thrust this Sword into Ganondorf's chest, intending to execute him; however, the attempt was in vain, as the Triforce of Power, which was in Ganondorf's hand, preventing him from being harmed by the Sword (although it left a glowing wound in his chest that would later become his weak spot). Ganondorf took the Sword from his body and killed the Sage of Water. Ganondorf kept the Sword for many years, using it in the final battle with Link.

Ganondorf stated he desired to use the sword from the sages who attempted to execute him to blot out light.

Super Smash Bros. Series
In, Ganondorf shows the Sword during one of his taunts. In, Ganondorf shows the Sword as a taunt once again. He can also attack with it by using the Warlock Blade, a custom neutral special move that replaces the Warlock Punch.

Trivia

 * While Ganondorf is wielding the sword in Twilight Princess, the color changes from white to a glowing red; while this may be just due to the lighting, its similar coloration in Super Smash Bros. could mean the color change is intentional.
 * Outside of non-canonical media, this is the only time Ganondorf has used a single sword instead of dual wielding a pair of swords, or using a trident.