Ness:
Beat the game on Normal with the number of lives set to three and without continuing. After the credits Ness will challenge you. Beat him and he will become playable.

Jigglypuff:
Beat 1 Player mode with any character.

Classic Mushroom Kingdom:
Beat the 1-player game with the 8 main characters and play on all eight arenas in Vs. mode. This opens up the Classic Mushroom Kingdom in Vs. mode.

Item Switch Menu:

Play Vs. Mode 50 times to open up the Item Switch Menu from the Options screen.

Borrow a life:
Begin a Team game in Vs. mode. Then if you lose a life, press Start to take a life from your partner.

Music Test:
Beat Bonus 1 & 2 with all characters (including secret ones) and a music test option will appear on the data screen.

Rotate Characters:
You can view the characters from different angles by entering the Character Bio section and holding Z. Use the analog stick to move them around.

Get Luigi:
Break all the targets and boarder all the platforms in 1-player practice with the 8 original characters.

Change Outfits:
You can change your character's outfits by tapping the C Buttons at the Character Select screen.

Beat Fox Without Getting Hurt:
To beat Fox without getting hurt you must get Captian Falcon. Then in one player mode (using Captain Falcon) get up to the fight with Fox. Next roll BACKWARD until you can't roll anymore. Then Fox will start to run at you. He will then start to do a sliding kick. When he's about to hit you do a double jump (triple if you have to). Fox will pause under you and fall helplessley to his doom. If Fox doesn't start to slide that means he will do an arial kick. Triple-jump over that.

To play these modes you need to play multiplayer. You must configure these yourself...

Star Wars mode.
players: Captain Falcon, any uniform
         Samus, any uniform
(c.falcon and samus must play against each other) if there ar to any more players there must be uone on each side.

items:Only beam sword and max. tomato.
Level: star fox home ground
Rules: no one must fight until every one has a beam sword, but if someone drops theirs, they may still be hurt.
Lives: 5
Time:none

007 Bond Mode
Players:Captain Falcon(Jaws), C right uniform
        Samus(bond), C down uniform
        DK (trevalen), C right
        Luigi (Miskin), c down
        Fox (boris), C right
        Mario (ouramov), c down
Items: Ray gun, motion sensor bomb, heart
Level: Links home kingdom
Rules: No one can fight until every on has a ray gun, if they hit someone without a ray gun, then they must commit suicide.
Lives: 1 
Time: none
Damage: 50 %

GameShark Codes

Enable Code (Must Be On)
de0004000000
f10396b02400

Infinite Time (Story Mode)
810a4b2e43cb

Infinite Lives P1 (Story Mode)
800a4b430004

Infinite Lives P2 (Story Mode)
800a4bb70004

Infinite Lives P3 (Story Mode)
800a4c2b0004

Infinite Lives P4 (Story Mode)
800a4c9f0004

Infinite Time (VS Mode)
810a4d1e43cb

Thanks to Revolution readers Kevin, Jason, Dane, Stormfront, Guerrand, Dan, Larry Hoffman, Magicman, Cody Hughes, Christopher Beers, Scott Steele, Rsayo, Gumby, Hunter Hendricks, A.N.W., Gohan, U|timate157, Destroyer, Aaron Illingsworth and Brad Cason, Norf!