S2E4: Alone Again, Unnaturally

Sonic and Tails are working on an invention to make Sonic even faster. Unfortunately, Sonic goes so fast that he eventually disappears. Tails is nervous. Did he disintegrate Sonic? Meanwhile, Sonic is alone in another plane of existence where he can only see ghostly images of his friends but can't communicate with them. When Eggman decides to attack, the gang battles him while protecting Tails so he can work on a solution.