It's been discovered by members of the Mobius Forum that Dr. FexusFan is a secret character in Sonic Riders! FexusFan is an unlocked when you run over all 16 daisies in the game. They're hard to find and there's one in each level including Sega Carnival and Illusions. Once completed, Extra 5 is unlocked with missions where FexusFan is used. There are a couple of screenshots with FexusFan that can be seen below.
