Super Mario Bros. Deluxe (GBC)
For more tips and tricks, please see the Super Mario Bros. codes.
This code will erase all your saved game data, including everything you've unlocked (e.g. photo album, medals, etc.). On the Select File screen in Original 1985 mode, press Start to bring up the Copy/Clear options. Hold Select and press A, and the game will ask, "Erase all data? No/Yes". Move the cursor down to "Yes," press A, and it's done.
Play as Luigi
In the Original mode, Challenge mode, and "SMB for Super Players" mode, press Select on the map screen to change Mario to Luigi and vice-versa. Unlike the Japanese SMB2, Mario and Luigi have the same abilities. If you used Luigi the last time you played, then you'll be Luigi the next time you enter the You Vs Boo mode.
In the "You Vs Boo" and "Vs Mode" level select screens, press Select and you can change Mario from small to Super to Fiery and back again.
Extra lives for everyone
All the invisible 1-Ups from Super Mario Bros. are available even if you didn't collect all the coins in the preceding x-3 world. They are in the same locations as before.
Start with 10 lives
In the Toy Box, play the Fortune Teller game until you get a "extremely lucky" fortune. Now go to the Original 1985 mode, start a brand-new game, and you will start off with ten lives in reserve instead of five.
Unlock "You Vs Boo" mode
Get more than 100,000 points in the Original 1985 mode, lose all your lives, then save your game. Go back to the menu screen and a Boo will now be there. You can now move the cursor down next to it and select it.
Unlock "Super Mario Bros. for Super Players" mode
Get more than 300,000 points in the Original 1985 mode, lose all your lives, then save your game. Go back to the menu screen and Luigi's head will now be there. You can now move the cursor down next to it and select it. SMBFSP is really the "SMB: The Lost Levels" game from Super Mario All-Stars, which is really the Japanese version of Super Mario Bros. 2.
Here's how to phill, er, fill up your photo album: