Play as Pan-Pan and Black Alien in versus mode:
Defeat Picwick for first time to unlock Pan-Pan and the Black Alien in versus mode.
Play as Lunk in versus mode:
After Pan-Pan frolf against and defeat Lunk to unlock him in versus mode.
Play as Pappy in versus mode:
Defeat Lunk, then go back to Ribbittron and defeat Pappy to unlock him in versus mode.
Play as Sir Waddlesworth in versus mode:
Defeat Pappy to frolf against Sir Waddlesworth. Win the match to unlock him in versus mode.
When playing on a field with water, Try using the extra Jumps and points to your advantage by aimming lower.
To unlock any character to use in VS mode, beat them in the single-player game.