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Unlock Dark Chao Garden
To unlock the Dark Chao Garden, you must raise a Dark Chao with one of the three ''Dark'' characters. Continually feed and train your Dark Chao and soon it will evolve (creates a tear-shaped ''cocoon''). Once it evolves, the descending stairs should appear at the main Chao lobby leading to the Dark Chao Garden.
Unlock Hero Chao Garden
To unlock the Chao Hero Garden, you must raise a Hero Chao with one of the three Hero characters. Continually feed and train your 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.
Boss Attack Mode
To unlock the Boss Attack mode, complete either the Hero or the Dark side story modes. Here you will be able to fight each boss from either the Hero or the Dark side.
Clear picture
When Pausing press and hold the Y and X buttons.
Get Alternate Costumes
Finish all of the character's (Sonic, Tails, Knuckles, etc.) missions. Then you will get an alternate costume for two player mode.
Guaranteed 'A' rank
An alternate way to get an 'A' rank on each stage is to collect every ring in it. It should say 'Perfect' next to your ring count at the end of the level and you will have an 'A' rank.
Secret Karts
Complete all of a characters missions for a secret kart for that character in Kart Racing.
Unlock Diamond & Onyx Chao Races
Win at least one race from Aquamarine, Garnet, Peridot, and Topaz Chao Races to unlock them.
Unlock Green Hill Zone
Get all 180 Emblems and unlock the 3D version of Green Hill Zone from Sonic The Hedgehog 1.
Unlock Jewel races
Complete all 4 of the original races and get the emblem. The Jewel races will be unlocked.
Unlock Kart Racing Game
In order to unlock the Kart game, in the Hero Side story complete the Tails driving quest and then in Dark Side story successfully finish the Rouge chase mission. You will now have a playable kart racing game to play.
Unlock the Last Stage
In order to play the actual last and final stage of this game, then finish both Hero and Dark side story games. Once this is done, go into story mode and a ''Last Stage?'' menu selection should appear between the Hero and the Dark Side selections.
Win Chao Toys
Shovel: Win all 3 Crab Pool races
Watering Can: Win all 3 Stump Valley races
Toy Car: Win all 3 Mushroom Forest races
Rattle: Win all 3 Block Canyon races
Big the Cat Appearances
There are several places in SA2 that you can see Big the Cat from the original Sonic Adventure Dreamcast game. Here are a few of them:
1. City Escape: About 3/4 of the way down when you're running away from the truck look on the right sidewalk to see him running away.
2. Radical Highway: After going in one of the rockets look at the blimp to the left and he will be sitting on it.
3. Pumpkin Hill: Go to the area where the train is stuck (it's going back and forth) and he is behind one of the gates waving to you.
4. Cannon's Core: With Rouge, go to the top of the highest pillar in the main room and look up. He's jumping up and down.
5. When you're battling against Shadow with Sonic in the Green Forest area there is a grate. Look down in the grate and you can see Big fishing.