Race Cars and 2P Skins
To unlock new race cars, complete every characters' missions. It doesn't matter what rank you get.
To get new 2P skins, get A-Rank on every mission. The skins will only be for Sonic, Shadow, Tails, Eggman, Knuckles, and Rouge.
We have more cheats and tips for this game here, Sonic Adventure 2 Battle cheats
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