Defeat Picwick for first time to unlock Pan-Pan and the Black Alien in versus mode.
After Pan-Pan frolf against and defeat Lunk to unlock him in versus mode.
Defeat Lunk, then go back to Ribbittron and defeat Pappy to unlock him in versus mode.
Defeat Pappy to frolf against Sir Waddlesworth. Win the match to unlock him in versus mode.
Collect 10, 20, or 30 Bottle Caps or complete any other task on the bonus disc.
After you defeat an opponent, sometimes they will give you an egg. If you buy the egg, after a short time it will become a frog. You are not notified of this, but if you keep checking back in Picwick, go to the Frogs section. The frogs you have hatched will be in there. Sometimes your opponents will also offer you items. Note: After defeating Sparky & Woosh 2, they may try to sell you some "Game Hints" book for 100,000. They will never offer it again -- it is recommended you buy it at that time if desired.