Its already available. To get each mode play through adventure mode and make sure you also set up your chao garden.
Chat with our AI personalities
Amy is already unlocked, just choose to play as her
unlock him by shagging the boss
In Sonic Adventure 2 Battle(she is very hard 2 unlock get all rank A's with sonic!)Sonic Adventure DX,Sonic Advance 1 2 and 3(in 1 of them you have 2 unlock her).Sonic Riders.
Keep earning emblems (80 I think...). Also, she is only available for two player mode, not the single player.
in sonic adventure dx you can only unlock metal sonic by collecting 130 sonic emblems.