The following is a list of all the secret weapons and their effects. The weapons listed can only be found by destroying the playing field. The message "Map Destroyed" will appear when you have destroyed everything that can be broken. Note: In the two secret stages, "Some Like It Hotter" and "The Raging Mouse", fields can not be destroyed, thus there are no secret weapons for them.

That Sinking Feeling: Octopus (if thrown hard, causes other player to petrify).
A Fridge Too Far: Rotten Eggs (poisons player when thrown)
Haunted Mouse: Pirate Sword (stabs player).
Liao Meow: Bee's Nest (stuns player when thrown).
Franken Mouse: Electric Bomb (shocks player when thrown).
Towering Inferno: Time Bomb (10 seconds to throw at other player;explodes on impact).
Paws: Electric Eel (shocks player when stabbed).
Luncheons And Dragons: Excalibur Sword (knocks player unconsousn when stabbed).
Snow Fight: Ice Barrel (freezes player when thrown)
Scrap Yard Scrap Up: Hammer (knock player unconscious in one hit).
Unfurgiven: Branding Star (Burns player to a crisp when stabbed).

On Luncheons And Dragons, hit anything that can be destroyed. When it says "Map destroyed", look for the sword in the rock to find the secret weapon. The same can be done on all levels for different weapons. Note: If you use Jerry, Nibbles. or Tom, you may get a costume on Lungens And Dragons. On the western level, you can unlock a costume with Tom, Nibbles, and Spike.