Silver
Fight Silver with Sonic, first do a slide move into him as he is falling from the sky. Now, collect a ring and run around until you hear "How bout this?", then do a homing attack on him. Run away again until you hear "How bout this?" again. then do a homing attack again. Repeat this until he is defeated.

Last episode
Complete Sonic, Shadow, and Silver's episode to unlock the Last episode.

Completion bonuses
Get a 100% completion for Sonic, Shadow, or Silver's episode to unlock the Audio and Theater room under the Extras menu.

Free mode characters
Complete the listed task to unlock the specified character in Free mode:

Amy Rose	Complete all Soleana mystery missions with an "S" rank.
Blaze the Cat	Complete all Soleana mystery missions.
E-123 Omega	Complete all GUN Commander missions with an "S" rank.
Knuckles the Echidna	Complete all Town Stage missions with an "S" rank.
Miles "Tails" Prower	Complete all Town Stage missions.
Rouge the Bat	Complete all GUN Commander missions.

Free mode
Get an "S" rank on all of Sonic, Shadow, and Silver's levels, Bosses, and town missions to unlock Free mode.

Shadow The Hedgehog
Complete Crisis City with Sonic to unlock Shadow's episode.

SUPER Fast Sonic
In Multiplayer mode in any level or match, equip the Red Gem on Sonic, activate it and hold it, then die. While still holding the activation button, wait until you respawn. When you respawn, deactivate the gem. You will now run much faster than normal and the time will automatically be slow. Kinda SUPER Fast now!

Silver The Hedgehog
Complete the Silver The Hedgehog Boss battle with Sonic to unlock Silver's episode.