Sonic The Hedgehog

Successfully complete Sonic, Shadow, or Silver's Story mode 100% to unlock the "Extras" option at the main menu with "Audio Room" and "Theater Room" options.

Successfully complete Crisis City as Sonic.

Win the Silver The Hedgehog Boss battle as Sonic.

Complete Sonic's Episode, Silver's Episode, and Shadow's Episode.

Complete the indicated task to unlock the corresponding 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.