Excalibur (エクスカリバー,Ekusukaribā?) is the transformation of Caliburn, created by merging with the three other sacred swords; Arondight, Galatine and Laevatein. Essentially an algamation of all the sacred swords, Excalibur is the original and greatest of all the sacred swords. Caliburn's transformation to Excalibur was caused due to Sonic's willpower. His "never give up" attitude rekindled the long lost light of Excalibur, allowing Caliburn to become Excalibur and Sonic to become Excalibur Sonic, giving them the power needed to beat the Dark Queen.
Of all the sacred Swords, Excalibur resembles mostly Caliburn's normal form, similar to a katana. Excalibur is gold and silver, then he gains a crown-like figure on his pulled back hilt with ruby in the center, and a glowing outer blade around his physical blade.
Long ago, Excalibur was originally guarded by Nimue, the Lady of the Lake, along with its scabbard. The sword itself rested in the lake in Deep Woods where it was held up by fairy magic. One day, however, a young King Arthur came to the lake to seek out a new sword to replace his broken one. Nimue decided to bestow both Excalibur and its scabbard to Arthur, because he had proven himself worthy of character to wield them. Excalibur eventually became King Arthur's personal weapon, and he used it to save the kingdom countless times. However, Arthur apparently never chose to wield it in public, or at least never in front of the Knights of the Round Table.
When Arthur began to be corrupted from being bewitched by the scabbard of Excalibur's power, however, the king's evil tainted Excalibur, transforming it into Deathcalibur. Though Excalibur's light was ultimately locked away, it was not the end of it, and it somehow split into the sacred swordsArondight, Galatine, Laevatein and Caliburn, though Arthur still managed to retain Deathcalibur. With Excalibur gone, the blade itself faded into legend.
In Sonic and the Black Knight, as Sonic confronted the Dark Queen, he was pummelled to an inch of his life and got Caliburn cut in half. Regardless, Sonic refused to give up, having resolved to stop Merlina no matter what. With Sonic's determination shinning brighter than ever, the lost light of Excalibur was reawakened within the sacred swords and Nimue had the Knights of the Round Table send their sacred swords to Sonic and Caliburn. The power of all four sacred swords then transformed Sonic into Excalibur Sonic and not only repaired Caliburn, but also transformed him into the true Excalibur.
With Excalibur reborn, Excalibur and Excalibur Sonic engaged the Dark Queen in battle, with Excalibur giving Sonic the means to counter the Dark Queen's magic. The duo eventually got the Dark Queen on the ropes and finally triumphed over her when Excalibur Sonic pierced her with Excalibur. After the battle, Excalibur reverted back into Caliburn.
"Can't you get in close somehow? We'd have a good chance to win if you could close the gap!"
"Listen carefully. Timing is everything! Swing your sword at exactly the right moment."
"You must wait for your chance to close in for the kill."
"You'll never get anywhere like this. Go full force with the Soul Surge!"
"Don't underestimate Excalibur reborn."
"I am going to teach you the error of your ways!"
"Everything must have it's end and we will be yours!"
"Foolish wizard! You're willing to sacrifice countless others just to escape your own sorrow?!"
"Hmph! You are mistaken if you think this is the limit of Excalibur's power!"
"Do you honestly think such a world would function properly?"
"She appears to be worn down, we might be able to get through to her now."
"There is nothing Excalibur can't cut through!"
On the hilt of Excalibur, the rubied hilt now resembles a crown, as well as the Black Knight's helmet. This is a reference to how Excalibur is the legendary blade of King Arthur, and Sonic just so happens to be the King Arthur of the game.
The power of Excalibur's Scabbard are similar to the real Arthurian Legends, except in the legends, the Scabbard would prevent any wound from bleeding or prevent death from a mortal wound. In the game, the Scabbard only prevents all wounds.
The glowing aura of Excalibur has a similar design to the Gran Faust and Divine Avenger from Spiral Knights.
The blade of Excalibur is golden in the game; however, it is pure white in its artwork.
Caliburn transforming into Excalibur.
Excalibur Sonic wielding Excalibur.
Excalibur Sonic extending Excalibur's energy blade.
Excalibur Sonic and Excalibur preparing their final attack.
Excalibur Sonic and Excalibur after defeating the Dark Queen.
↑Sonic Team (March 13, 2009). Sonic and the Black Knight. Nintendo Wii. Gallery. Vault 5. [Excalibur] "When Arthur broke his sword, Merlin guided him to the lake where he found a sword held aloft by fairy magic. Arthur went out in a small boat and claimed the sword. That sword was the legendary Excalibur, which Arthur used to save the kingdom countless times."
↑"The legendary king and ruler of Camelot, King Arthur has been corrupted by mysterious forces and now rules as a tyrant over the tainted land. His enchanted sword has been transformed by this evil, becoming Deathcalibur. With his army of minions, he appears unstoppable until a certain blue hedgehog arrives." - Sonic and the Black Knight website.