First to get King you have to beat all normal matches and all training games in world circuit to unlock a level 4 match against King. After you beat him you'll unlock a doubles match against King and Master. After you beat that final match you'll get King to use in arcade and exhibition matches. To get Master you must play arcade mode on very hard (might be able to get on normal also not sure I only play very hard) and win every single game and set straight through, you cannot lose any games or matches if you do it will not work. After you beat the last guy you'll see your character celebrate and then it will say new challenger, it will be Master. Beat him and you'll now be able to use Master in arcade and exhibition modes. To make this easier you can put the amount of games on 1 the number doesn't make a difference on the amount of money you get or affect facing Master after the last guy. Heres a few pointers on Master first he doesn't have 150mph serves like King but he'll throw you some tricky serves that go slower then they look just be ready to move up on them and swing do that and you'll have really no problem beating him hes not really harder then most of the other characters as long as you don't make bad shots which he'll burn you on, as for King the only real problem with him is the 150mph serves you just have to be real fast and judge it very good and move up on it at the right time other then that hes easier then Master to beat.