Hi in the game sonic adventure 2 battel my chao reached maturity and it was not a holy chao or a devil chao it was larg and green keep in mind it was a normal noncolored egg this still baffels me could pleas tell me what this could be and how it happened?
Sounds like you have a Neutral/Swimming chao, or possibly Neutral/Running. Evolved Neutral chao can have all sorts of colours and markings.

~ Crazy C Lea