Sonic Adventure Cheats - PlayStation 3
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Unlock Characters
Amy - Talk to her in the Casino as Sonic after finishing Sky Chase.
Big - Defeat Chaos 6 as Sonic.
E-102 Gamma - Defeat Gamma after finishing Sky Deck as Sonic or Tails. An alternate way to unlock him is to finish Twinkle Park as Amy and watch the FMAs after it.
Knuckles - Defeat him after finishing Ice cap as Sonic or Tails.
Miles Tails Prower - Finish the C mission of Emerald Coast action stage as Sonic.
Metal Sonic - Collect all 130 emblems and visit Trial mode and pick Action Stage (Requires Sonic Adventure DX Addon).
Super Sonic - Finish the game as Sonic, Tails, Knuckles, Amy, Big and E-102 Gamma. Super Sonic will be avaliable only in Adventure Mode.
Unlock Upgrades
Ancient Light (Sonic) - On top of a rock on Angel Island.
Booster (E-102) - In the Weapon's Armory on the Egg Carrier.
Life Belt (Big) - In the entrance to Icecap.
Light Speed Shoes (Sonic) - Find it in the sewer (not the onebehind Twinkle Park).
Lure Upgrade 1 (Big) - In the sewer behind Twinkle Park.
Lure Upgrade 2 (Big) - Under an sheet of ice in IceCap.
Lure Upgrade 3 (Big) - In a cave in the forest.
Lure Upgrade 4 (Big) - In one of the jail cells on the Egg Carrier.
Long Hammer (Amy) - Beat your own high score on Hedgehog Hammer after the Egg Carrier crashes.
Crystal Ring (Sonic) - Walk up the steps in the hotel, press the two buttons and use light speed dash.
Fighting Gloves (Knuckles) - On a ledge over Big's house.
Jet Anklet (Tails) - In a hole in the ceiling in the sewer behind Twinkle Park.
Laser Blaster (E-102) - In the Restricted room on the Egg Carrier after it crashes.
Long Rod (Big) - Under the bed at Big's hut.
Rhythm Badge (Tails) - In the flashback with Tikal.
Shovel Claw (Knuckles) - In the tunnel inside the tunnel where you find the cart to the Mystic Ruins Chao Garden.
Warrior Feather (Amy) - Beat Eggman's high-score on Hedgehog Hammer.
Play Emerald Course in Chao Race
Beat the rest of the four courses. Note: Don't delete your your chao data or else you will have to do them again.
Easter Eggs: Experience a Short NiGHTS Homage
While playing with Sonic in Casinopolis, go to the pinball game with the NiGHTS motif. Hit the three little purple point givers in order to open up an entrance at the top of the board. Then make your way through the secret entrance. You'll now be in another NiGHTS motif pinball game. Whenever you fail to catch Sonic with the bumpers, don't worry about losing a ball. Instead, Sonic will be transported through a world very familiar to the NiGHTS level Splash Garden.
Playstation Home Unlockables
Light-Speed Shoes - Unlock the light-speed shoes in-game, then upon loading the savefile after booting the game a second time it will unlock in Playstation Home.
Sonic Adventure T-Shirt - Create a savedata for the game and load the game and savedata at least once.