Pan-pan And Black Alien
Defeat Picwick for first time to unlock Pan-Pan and the Black Alien in versus mode.

Lunk
After Pan-Pan frolf against and defeat Lunk to unlock him in versus mode.

Pappy
Defeat Lunk then go back to Ribbittron and defeat Pappy to unlock him in versus mode.

Sir Waddlesworth
Defeat Pappy to frolf against Sir Waddlesworth. Win the match to unlock him in versus mode.

Unlocking Clips
Collect 10, 20, or 30 Bottle Caps or complete any other task on the bonus disc.

Unlocking Character
To unlock any character to use in VS mode, beat them in the single-player game.