One possible plot could be Sonic facing a new, more powerful enemy in the Arthurian world. Maybe a dark wizard has emerged who is corrupting the magical elements of the land, and Sonic has to race against time to stop him before the entire realm is plunged into eternal darkness.
The plot could also involve Sonic's relationship with the characters from the first Sonic and the Black Knight. For example, Sonic might have to deal with a rift between him and one of his Arthurian allies. This internal conflict, along with the external threat of a new breed of dark knights, would add depth to the story as Sonic tries to resolve the issues and save the day.
In Sonic and the Black Knight story, Sonic is transported to a world based on Arthurian legend. He has to face various challenges and enemies while on a quest. He wields a sword and battles against the Black Knight and other foes to save this new world.
Well, one possibility could be that Sonic and Eggman are forced to team up against Black Doom. Maybe Black Doom is threatening to destroy their world, and they realize that only by combining their strengths, Sonic's speed and Eggman's technology, can they stand a chance.
One idea could be Sonic having to face a new dark version of himself created by the Black Knight's magic. This dark Sonic could have different powers and a more menacing attitude, making the battles even more intense.
One idea could be a new character being introduced into the Sonic Black Knight world. This character could be from another dimension and have unique powers. They could initially be seen as a threat but end up teaming with Sonic to fight a greater evil. Another plot could be Sonic losing his sword skills and having to go through a series of challenges to regain them, all while facing off against old enemies with new twists.
A corrupted King Arthur could be the new villain. Imagine if the power of the Excalibur sword has turned him evil, and he now wants to rule the world with an iron fist. Sonic would have to find a way to break the curse on Arthur and stop his tyrannical rule.
One plot idea could be Lancelot training Sonic in the ways of the knights. Since Lancelot is a skilled knight, he could teach Sonic about honor, chivalry and different combat techniques. This would be interesting as Sonic's fast - paced and impulsive nature would contrast with Lancelot's more traditional and disciplined approach.
One idea could be Sonic having to face a new and more powerful dark version of the Black Knight. This would test his skills and force him to find new ways to use his speed.
The main antagonist could be an evil sorcerer who has corrupted the Black Knight and is using him to carry out his dark plans. This sorcerer could be after Sonic's speed power to enhance his own magic.
One possible plot could be that there is a powerful new item in their world. Sonic thinks it should be used immediately to stop Dr. Eggman, but Tails believes they need to study it more first. This disagreement leads to a fight as Sonic tries to take the item by force and Tails tries to stop him.
How about a magical mermaid who lives in a hidden lake in the world of Sonic and the Black Knight? She could have the power to heal Sonic when he's injured and give him clues about the secrets of the Black Knight's sword, but she also has her own motives and secrets that Sonic has to figure out.