• Alternate costumes

Highlight a character on the selection screen, then press B. | [Sent by DayleJ]
  • Play as Ambia

Defeat the three opponents in the first tournament in tournament mode to unlock an amoeba player which turns into a racquet when hitting the ball. | [Sent by DayleJ]
  • Play as Kaoru

Defeat your opponents for the Aries cup in tournament mode to unlock a fat player. | [Sent by DayleJ]
  • Play with the ball

Press Down before serving, to bounce, toss, or do something else the ball (depending on your character). There is only one animation per character, but most characters' animations are unique.