Excalibur



Effectively a super transformation of Caliburn the Sword, Excalibur is (probably) the most powerful magical item within the Arthurian realm of Sonic and the Black Knight, as the strongest of the Sacred Swords.

Caliburn's transformation to Excalibur was caused due to Sonic's willpower. His "never give up" attitude rekindled the light of the Sacred Swords, and they were both empowered. Caliburn became Excalibur, Sonic became Excalibur Sonic to fight the Dark Queen, Merlina the Sorceress' powered up form. Excalibur has rubies in its hilt, and a glowing outer blade around Caliburn's physical blade.

Scabbard of Excalibur
The Scabbard of Excalibur is essentially the cause of all Grand Kingdom's woes in the first part of Sonic and the Black Knight's storyline. Given to King Arthur (during his noble days) by Nimue, Lady of the Lake, the scabbard bestowed immortality upon its bearer - a great power which corrupted the once just and valiant ruler into a demon-summoning tyrant.

Sonic's quest across the kingdom, from Misty Lake to Faraway Avalon, sees him gathering the skills and knowledge necessary to counteract the power of the Scabbard and thus be able to slay King Arthur.

Trivia

 * 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 sword 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 Arthurean 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.
 * Strangely, Excalibur speaks in third person.