I can't find find professor Banner or the abandoned dorm before the last..

When you try to go to sleep one night, Jaden will knock on your door and will tell you that you must go to the abandoned dorm and proffesor banner(Amanel) will be there to duel you. It's an endless night, so you can battle weaker duelists as much as you want, level up, and get stronger so you can beat him if you find him too hard. After you beat him, you must go to the eastern part of the island and beat Kagemaru's three decks at the seven spirit gates. Then, the shadow riders are gone, but can be re-dueled after you win the school duel against Chazz. In that, there's a best 2/3 round of duels. There are two or three duels with you and Chazz, and if you win the majority of them, you win. Also, keep in mind you can exchange cards with your "side deck" between duels so you can improve your chances of winning. You can have up to 15 cards there. After that, play until you get all the cards in the game.