Unlike most of Sonic's other transformations, Sonic himself does not undergo any physical change. Instead, he dons shining golden armor covering his entire body (except for his tail), and he carries Excalibur in his right hand. A red cape runs down the back of his armor.
Powers and abilities
In this form, Sonic is renowned as the ultimate Knight, hinting a high level of skill and power. He has increased strength, allowing him to deflect the large and massive sword strikes from the Dark Queen, and the ability to fly, along with the ability to use his own Soul Surge attack. He also gains a move similar to his Quick Step, allowing him to roll to the right or left to evade attacks. His attacks are also more close-combat based, as opposed to the boosting and energy moves that Super Sonic uses, and he can channel golden energy into his strikes for more devastating damage.
As Excalibur Sonic, Sonic wields the legendary Excalibur, the greatest of all the sacred swords. With it, Excalibur Sonic can cut through anything and deflect magical energy projectiles. He can also use Excalibur for his most powerful attack where he thrusts Excalibur directly through his opponent, while enveloped in a golden energy orb, making him resemble a golden meteor.
"What good is a world that goes on forever? That sounds pretty lame." - Sonic stating his reason to defy Merlina, just before battling her.
"Argh! Dodging to the right or left's the only way." - Sonic during the boss battle.
"Nah, it's not gonna end. My stories only end when I stop running!" - Sonic response when Merlina asks him, if he wants to see the Arthurian realm come to an end.
"Good, 'cause I don't ever want to know such one-sided sadness." - Sonic's response to Merlina when she proclaims her sadness about the kingdom's future.
"Heh heh! My trusty sword's gonna teach you a lesson." - Sonic backing up one of Excalibur's quotes.
"Yeah, it was a shocker for me too!" - Sonic explaining his reaction to Caliburn's transformation.
"I already told you, I don't mind playing the bad guy every once in a while." - Sonic reminds Merlina of his earlier statement in the game.
"What I can't understand is how you can call such a boring sounding place 'magnificent'." - Sonic telling Merlina his thoughts about her ideal kingdom.
Excalibur Sonic is the first transformation where Sonic's fur does not change color.
Unlike the super transformation, Excalibur Sonic does not need Ring energy to sustain his transformation and does not lose rings as time passes. Instead, he starts out with hundred Rings and loses twenty Rings for each hit.
Excalibur Sonic may not even be Sonic's transformation, but Caliburn's, because Sonic is only in a golden suit of armor, while Caliburn looks indistinguishable from his appearance in the rest of the game. Also, Sonic did not absorb anything to transform and is not invincible.
Jazwares did not make a figure of Excalibur Sonic until more than three years after Sonic and the Black Knight was released.
Sonic's quills wave while in this form, suggesting that the armor is quite flexible.
Coincidentally, there's a red jewel on the middle of Sonic's forehead. Merlina also wears a red jewel on her forehead and both of them are empowered by Excalibur.
↑Sonic Team (March 13, 2009). Sonic and the Black Knight. Nintendo Wii. Gallery. Vault 1. [Excalibur-Sonic and Excalibur] "Behold the golden light and mighty grandeur! The ultimate Knight, Excalibur-Sonic!"