King's Court will be unlocked if you defeat King and Queen (mixed double) level 5 in world tour mode. This level 5 will only be available if you won the mixed double match in level 4. These both matches will be in December.
Special rackets
In the world tour mode, defeat opponents in level 3 and higher without losing a set. If you win a straight set you will get a special racket in every championship that you won.
Play as King or Queen
Win all matches without using any continues. If using a male character, you will face King. Otherwise, you will face Queen. Defeat them to unlock them as playable characters.
Alternate costumes
Hold L1 or R1 and select a character at the selection screen.