How do you get a sonic chao in sonic adventure 2 battle

Well, when you go through a stage, there are boxes hiding around with a chao symbol on them. The first one you break, you get a key. Once you finish the stage, you can enter chao world and it becomes accessable through stage select (:
The 2nd box- animals (to feed ur chao)
the 3rd box- a mythical animal (to feed chao)