There are three new pieces of in-game content for Sonic available on Xbox Live Marketplace. The episodes are all 150 MS points and available in all Xbox Live regions for Xbox 360 owners. The details:

Name: Additional Episode "Sonic Boss Attack
Dash Details: Play Consecutive Boss Battle Mode for Sonic. You need to complete Sonic Episode to play all the stages in this mode.

Name: Additional Episode "Shadow Boss Attack"
Dash Details: You can play Consecutive Boss Battle Mode for Shadow. You need to complete Shadow Episode to play all the stages in this mode.

Name: Additional Episode "Silver Boss Attack"
Dash Details: You can play Consecutive Boss Battle Mode for Silver. You need to complete Silver Episode to play all the stages in this mode. There are no refunds for this item.