URGENT sonic adventure 2 battle chao question, PLEASE READ!!!?

In sonic adventure to battle I heard if you give your chao a bat it will have a genie tail I thought it would look good on my dark chao, Chai. I hate it! I read on gamefaq that to get rid of it you have to get a sea monster like the one in the black market at the chao kindergarten I have looked everywhere! where do I find this sea monster?