Instructions
Play through Sonic's Story Mode until you reach "Act 4: Crisis City."
Play through the hoverboard area. Use the board to grind down rails, make jumps and avoid your enemies. At the halfway mark, Sonic loses his hoverboard and has to proceed on foot.
Play through the super speed area. Sonic runs much faster than the hoverboard travels, which makes it difficult to avoid the cars that are flung at you at random intervals. Avoid the enemies when you can and focus on collecting rings and maintaining your speed.
Watch the cutscene at the end of the level. Completing the level unlocks Shadow's playable episode at the main title screen.