How To Easily Beat Colleseum Mode
First, you must unlock Kent and become a rank B, then get the best attack type parts you can (Sagitario has terribly low defense, and can rarely use a special attack), then go to the Colosseum mode, pick Kenta as your opponent, then choose the dead or alive stadium (A. Because there is no possible way to get a stadium out so Kenta won't be able to fight back, and B. The stadium is small so Sagitario can't dodge your attacks) when you beat him, hit resume, then back twice so you can choose Kenta and the dead or alive stadium again, and keep repeating as many times as you like.
HOW TO BEAT CROW
Get Tornado Wall and get near the edge. Hopefully Crows Bey will come to you and will right right out of the stadium!