Bonus characters:
Successfully complete story mode to unlock more playable characters.
Play as Big The Cat:
Purchase all pictures of Tails in Sonic's room to unlock Big The Cat in versus mode.
Play as Chao:
Purchase all pictures of Knuckles in Sonic's room to unlock Chao in versus mode.
Play as E-102 Gamma:
Purchase the last picture of Amy in Sonic's room to unlock E-102 Gamma in versus mode.
Play as Super Sonic:
Purchase all pictures of Sonic in Sonic's room to unlock Super Sonic in versus mode.
Notebook:
Successfully complete the game and enter Sonic's room to find the Notebook on the table.
Hidden artwork:
Place the game disc in a PC compatible CD-ROM drive to find artwork from the game in the "Sonic Shuffle" folder.