Sonic and the Black Knight is a Wii video game released in March of 2009. Many of the people who had worked on Sonic and the Secret Rings also worked on this game. While it carries some of the same elements from the first game, there are many new additions. The most notable addition is a sword that Sonic can use to fight enemies and perform special moves.
This game was created by a worker that worked with Sonic and the Secret Rings, right before the release date for it, thought "Won't Sonic wielding a sword be cool?" Then, that idea was expanded into this game.