Sonic Shuffle

Secret images:
If you insert your game disc into a PC CD-ROM drive, you will find
lots of images from the game in the "Sonic Shuffle" folder.

Notebook
Finish the game once after go to Sonic's room. You should find the
Notebook on the table.

Bonus playable characters
Finish story mode once

Unlock Chao in versus mode
Buy all pictures of Knuckles in Sonic's room

Unlock E-102 Gamma in versus mode
Buy the last picture of Amy in Sonic's room

Unlock Super Sonic in versus mode
Buy all pictures of Sonic in Sonic's room

Unlock Big The Cat in versus mode
Buy all pictures of Tails in Sonic's room