Borrow a Life: When playing a team multiplayer match, if you are defeated, but your team mate still has 1 or more life in stock. You can use one of his life to get back in the action by pressing A+B+Z+Start. Be sure to ask for permission from your friend.
Item Menu in the American Version: Play the versus mode 50 times to open this option. You will be able to select the number of times items appear and be able to select the items that appear.
Item Menu in the Japanese Version: Go to Vs. Mode, pick any 3 computer players and your favorite character to play. Play the "stock" mode, and set the lives to 10. Change the computer handicaps to 5. Play, if you are the victor, to you go the spoils! Enter options under vs., then go to items switch. You can choose what items will show up and how often they do. Bob-ombs galore! Infinite hammers!
Change Outfits: You can change your character's outfits by tapping the four C Buttons at the character select screen. Some costume changes are limited to colors, but characters like Pikachu are also available with a hat.
Classic Mushroom Kingdom: To access the hidden classic Mario stage (complete with POW signs, Piranha plants, warp tubes and elevator), beat the game's one-player mode with each of the original eight characters. It's important that you have the difficulty set to normal and stock set to three. At the end, the game will tell you that you can now access Classic Mushroom Kingdom in the versus mode.
Get Mew in your Pokeballs: After you get all 4 secret characters, (Luigi, Ness, Captain Falcon and Purin) you can find Mew in your Pokeballs! It takes a little bit of time, but you'll see one. If you have the Secret Item Menu, set it to all Pokeballs and it will be easier, or go to training mode. Mew has no apparent effect on the battle.
Item Menu: Go to Vs. Mode, pick any 3 computer players and your favorite character to play. Play the "stock" mode, and set the lives to 10. Change the computer handicaps to 5. Play, if you are the victor, to you go the spoils! Enter options under vs., then go to items switch. You can choose what items will show up and how often they do. Bob-ombs galore! Infinite hammers!
Kirby's Power Loss: Everybody knows that Kirby can swallow his opponents and take on some of their powers in this game, but what if you accidentally "ate" a character you didn't want -- and you want to pursue someone else? Simple: Just press the L Button to pull of Kirby's "Hello!" taunt and he will discard whatever power he took on.
Music Test: Complete Bonus 1 & 2 with all characters including secret ones and a "music test" option will be on the data screen
Play as Jigglypuff: To play as Captain Falcon, simply beat the one-player game in under 23 minutes.
Play as Luigi: To play as Luigi, pass the Bonus Practice 1 with at least 8 main characters. When Luigi challenges you, defeat him and he's yours.
Play as Ness: To play as Ness (from Mother 2, EarthBound), beat the game on Normal difficulty without continuing. This trick won't work if you change your number of lives. It has to be set to 3! After you have beaten the final boss, wait for the credits to finish rolling -- then fight Ness. Once you beat him, he will become available on the character selection screen. Play as White or Black Kirby At the character select screen, highlight Kirby and follow the codes:
To play as white Kirby, hold L button and tap C-Left and C-Up. To play as black Kirby, hold L button and tap C-Down and C-Right.
Rotate Characters: You can rotate and view the characters from different angles by entering the character bio section and holding Z. You can use the analog stick to move them around.