Haha, "turn your Game Boy upside down," that was good :D
Here's one I saw a long time ago for playing Peach, not Luigi, in SM64.
Peach in SM64:
Beat the game with 119 stars. Then get the last star and beat the game without saving. When you restart your game, you should only have 118 stars, but the cannon outside should be open. Launch yourself to the roof, talk to Yoshi, get the 100 lives and the fancy triple jump, and backflip from there to the lake. Now here's the hard part. Carefully lift the left side of your cartridge a little bit until the music changes to the DK64 theme. Then put the cartridge back in and save. Restart the game again, but while the screen is on Mario's face, take out the SM64 cartridge and put in the DK64 cartridge. Turn the power off and on again. (Note: Don't press the reset button because that won't work.) You should be playing DK64 with Mario. Beat the game with Mario, then quit and start up SM64 again. There should now be a giant star outside the castle. Get the star and you should be transported into a black room with Peach in it. You can't do anything with her, but if you walk out the door on your right, you will emerge from the castle doors outside as Peach!
This person was a much better speller than that other person with the Pokemon Red code.
The reason I remembered all that is that I actually printed it out and tried it. It didn't work, of course, and fortunately, it didn't harm my games, either. Keep in mind, this was back when the N64 was still young enough that not many people had beaten SM64 with all 120 stars.
Bozone, n.:
The layer of gas surrounding a person which prevents good ideas from penetrating.