Negating the immortality brought by Scabbard of Excalibur
A magical sword which is said to never lose its edge
Arondight (アロンダイト,Arondaito?) is an item that appears in Sonic and the Black Knight. It is one of the unlockable weapons in the game that can only be equipped to and wielded by Sir Lancelot. It is Lancelot's signature sword and is one of the Sacred Swords found in the world of Camelot. While Arondight can be wielded normally, Lancelot chooses to wield it with a backhand grip. It is said that the blade of Arondight never loses its edge. It is the first sword that Sonic collects in the Adventure Mode of the game.
Arondight is a single-edge, dark-colored sword, with a semi-serrated edge and a web-like pattern near the point. On the blunt side of Arondight extends eight pointy metal layers, while the guard has another metal layer with a claw-like extension in front. The grip itself is white and thin, with a golden decorated top and a pointy sword pommel.
I.D. Point Price: N/A
Rarity Level: 0/10
Item Type: N/A
Location: Deep Woods (Mission "Defeat the Boss: Sir Lancelot")
The following Skills are equipped to Arondight. When Arondight is equipped to Lancelot, he obtains these Skills.
Press the B button when there is energy in the Soul Gauge.
In Sonic and the Black Knight, Arondight had been in the possession of Sir Lancelot for an unprecedented amount of time. It is possible, though, that Arondight might have originally been a part of the legendary sword Excalibur, but was then divided into Arondight and the other Sacred Swords when Excalibur's light was lost.
Shortly after Sonic the Hedgehog's arrival in the Arthurian realm, Lancelot was sent out on a mission by King Arthur to find both Sonic and Merlina the Wizard and kill them on sight. Lancelot was the first of the knights to find Sonic and challenged him to a sword duel, where Lancelot used Arondight and Sonic used Caliburn. Because he underestimated Sonic, however, Lancelot was quickly defeated and Sonic took Arondight with him.
Sonic later used Arondight in conjunction with Galatine, Laevatein and Caliburn to neutralize the immortality granted by the Scabbard of Excalibur during his final battle with King Arthur and succeeded, thus allowing Sonic to finally defeat the evil king.
When Merlina betrayed Sonic and tried to take control over the kingdom, Sonic gave Arondight back to Lancelot, who used it to help the others set up a barrier to contain Merlina's power, though the barrier proved to be too weak. Finally, Arondight was used along with Laevatein and Galatine to help Sonic transform into Excalibur Sonic and Caliburn to transform into Excalibur.
Real World Background
Although Arondight is nowadays commonly claimed to be the name of the sword of Lancelot, it was never referred to by this name in any surviving piece of Arthurian fiction. The name first appeared in a Middle English metrical romance (dating around the 14th century) about Sir Bevis of Hampton, in which it is used by Sir Bevis' son, Sir Guy. The sword, whose name is written Aroundyȝt (or Aroundight) is described only briefly as the sword that "was Lancelot's du Lake, therewith he slew the fire-drake" (that is, a sword Lancelot used to kill a dragon). The poem further describes Aroundight as having a pommel made of carbuncle, and says that it is the finest sword that ever existed.
The name was eventually taken up by writers such as Longfellow, in his Tales of a Wayside Inn (in which it was mentioned alongside other famous swords), and appeared as the name of Lancelot's sword in Brewer's Dictionary of Phrase and Fable.
In the legends, Arondight was supposedly created by The Lady Of The Lake from the stars and was created as a sacred sword. However, when Lancelot killed Gawain and his brothers, the blade became cursed rather than sacred. 
Arondight is the only inanimate sword to have its name mentioned in the game's cutscenes.
Arondight is sometimes referred to as the Sword of the Lake, due to Lancelot being the Knight of the Lake.
Lancelot holds Arondight in reverse grip, and is the only knight to do so.