Complete Arcade mode without losing a game as a male tennis player. Instead, of an exhibition match appearing at the end Arcade mode, a special match message will appear. You will face Duke; defeat him to unlock him as a selectable character.
After you reach the ranking of Tennis Hero (600 stars), you unlock a t-shirt of a tennis playing super hero, Tennisman. If you win a tournament while wearing the shirt, Tennisman himself will send you fan mail.
In World Tour Mode, complete the fourth toure with over 750 stars (Ultimate Star ranking) to be invited to a special bonus tour. Included in this tour is an incredibly difficult match against a well dressed Brit in a regal, baroque style ballroom/tennis court.
On the match screen where you chooset the tennis players to use, select LOAD. This will list down the players you have in the career mode. From this screen, press + to select Vickie Virnie or press - to select Theron Tenniel.
In Arcade mode, your score is based on how many points you score on your opponent. Kicking your opponent's butt will actually earn you less points than if you force a deuce (tied 40-40) and keep going back and forth for as long as possible.