Dark Garden
Raise a Dark Chao with one of the three Dark characters. Continually feed and train the Dark Chao and it should evolve (creates a tear-shaped "cocoon"). Once it evolves, descending stairs should appear at the main Chao lobby leading to the Dark Garden.
Hero Garden
Raise a Hero Chao with one of the three Hero characters. Continually feed and train the Hero Chao and it should evolve (creates a tear-shaped "cocoon"). Once it evolves, ascending stairs should appear at the main Chao lobby leading to the Hero Garden.
Chao Ball
To win the Chao Ball for the Dark Garden, come in first place in the second Dark Race. You will find a new, creepy looking Chao Ball in the Dark Garden.
Kart racing mini-game
Successfully complete Tails' driving quest in the Hero side story to unlock the kart racing mini-game in the Hero side story. Successfully complete Rouge's chase mission in the Dark side story to unlock the kart racing mini-game in the Dark side story.
Boss attack mode
Successfully complete the Hero or Dark side story modes to unlock boss attack mode. You will be able to fight the bosses from the side of the story you completed.
Last stage
Successfully complete the Hero and Dark side story modes. Then, enter story mode and a "Last Stage?" selection will appear on the menu between the Hero and Dark selections.
Play as Super Sonic and Hyper Shadow
Successfully complete the "Last Stage?" in story mode to unlock Super Sonic and Hyper Shadow.
Full pause screen
Pause the game and press Y + X.
Hidden artwork
Place the game disc in a PC compatible CD-ROM drive to find several rendered images from the game.
New Chao races
Beat all 3 levels of the 4 Beginner Races (Crab Pool, Stump Valley, Mushroom Forest, and Block Canyon) to open Jewel Race and Challenge Race.
Quickly complete Security Hall stage
In the Security Hall stage you play as Rouge The Bat and are given 5 minutes to complete it. This can be quite difficult. If you have enough lives you can do this trick. If you cannot seem to find the Emeralds, intentionally die. You will keep the existing Emeralds that you have collected. You will begin at the start of the level and the Emeralds will move to different places. This is the fastest method for completing the stage if you are having trouble.
Big The Cat appearance
In Knuckles' Pumpkin Hill level, go to the one of the train gates. You can see Big The Cat hiding behind the gate, waving to you. You can also see him in the battle against Sonic while playing as Shadow.
E102 appearance
In Rouge's Inside the Pyramid stage, one of the robots you blow up is E-102.