Chaos the Chao God
To unlock chaos as a player, you must be in the emerald episode. first go to the shrine and you will speak to knuckles. then go north east to the crater area. chaos will be there. he will say ... and you say yes if you want to fight him. you must get 10 points [K.O. Battle] and you will get one of his move and unlocked him in challenge mode and battle mode and other modes.
How to unlock E-102, Tails, and Rouge
To unlock Gamma, play through story mode with Sonic until you reach Holy Summit. Go to the plains. Press A and a cutscene will go on. You will fight Gamma in a 5 KO battle. defeat him, and you will fight him in a 10 KO battle. Beat him, and you can play as Gamma in battle mode. To unlock Tails, beat story mode with Sonic. To unlock Rouge, beat story mode with Tails.
Unlock Rouge in Story Mode
Complete Tails' episode in Story Mode.
Unlock Tails in Story Mode
Complete Sonic's first episode in Story Mode.