Big the Cat in Sonic Adventure 2: Battle

I'm new here. I hoped someone could help me with a problem I had on Sonic Adventure 2: Battle.

I found on the Internet that there are supposedly several places you can spot Big the Cat. I tried almost everything, for example it said that on the Weapons Bed level (as Eggman) Big is sitting on top of the first garage with TNT packs on it. I jumped on the jet and couldn't see anything on the garage. I did almost every stage they listed but couldn't see Big anywhere. Am I doing something wrong? Are you supposed to beat the whole game first? I've only beaten the Dark story mode and am on the stage Crazy Gadget in Hero Mode.