I heard in the game that there is one secret mission that is really easy to get in the game Sonic Unleashed. All you have to do is to get S-Rank in every single mission and collect all Sun Medals and all Moon Medals. Once that is done with,go to Adabat and it's time to do the Final Mission,you will beproud once you finish this mission which means you beat Sonic Unleashed one-hundred percent complete. Happy cheating out there.
When you have completed ALL the missions with S-Ranks the game's final mission will become unlocked. Find the hidden item and complete this mission and you will be able to view the 'Sonic Omake' cutscene.