I remember this toric when I was lurking. I'll do couple quick ones for now:
Turn the game into a First person shooter:
First, go out and buy a handgun. Then, erase all your progress in every file on your game so far. Begin the game on file B and only file B. It won't work on any other file. After you hear Peach's letter and you take control of Mario, go to the first mission of Bob-omb Battlefeild. Find a Goomba, and keep running around him in circles over & over again ten times. Pull out your gun, because as soon as you circle the Goomba the tenth time, a water bomb will drop on Mario. The trick is to shoot your N64 the second the water bomb hits Mario. If you accompish this, you bullet you fired will appear on screen out of nowhere, still traveling from wence you fired it, and hit Mario. If Mario survives, then make him face the camera. Press and hold the C-up button. The Camera will zoom in on Mario's face. Eventually, the camera will clip through Mario's face, at witch point you will actually see through the eyes of Mario. Press the button you'd use to make Mario punch to fire a fireball. Congratulations! You are now playing SM64 as an FPS.
Play as the Burger King:
Take out the SM64 cartrige and shove a Whooper from BK in the cartrige slot. Place the SM64 cartrige in the cartrige slot while the burger is still in. Turn on the N64. When you hear Mario say, "Its-a me, Mario!" Hold down the R trigger and do not release until I say so. Select a file to play. release the R trigger. When you're in control of Mario, get up to the Castle rooftop by any means EXCEPT blasting up there in the cannon. If you use the cannon, your SM64 cartrige will implode. Once you've gotten up to the castle rooftop, punch the ! box to get the wing cap, which will allow you to fly. Fly over to the castle's right tower and fly through one of the tower's windows. Flying through any of it's windows will cause Mario to break through the glass, and appear in a secret room inside the tower. The room is tall and has no defining features/furniture, except a painting of the Burger King. Jump into the painting to be transported to a new level. This level is the exact same as the level, "Bowser in the Dark World", except all the Goombas have been replaced with walking burgers. When you get to the boss of the level, you'll discover not Bowser, but the Burger King. He'll explain that he killed Bowser, and he wants to kill Mario next. The battle will begin. His only attack is to chase after Mario trying to grab him. If he succeeds, he will force-feed Mario burgers until his artiries (sp?) are clogged up from cholesteral consumption, and Mario dies. You can beat him by grabbing the back of his robe, and swinging him around like Bowser until you throw him off the battlefaild. However, if you beat him, he will be gone for good and you will never have a second chance to unlock him. Instead, let him beat you. When Mario dies, the Burger king will say, "Oh, I killed Mario. I guess someone has to take his place...". The game will automatically turn off. Turn it back on, and the Burger King will replace Mario as the playable character. He plays the exact same as Mario, except when you stop for a long time, the Burger King will sit down and start eating burgers as opposed to sleeping like Mario. The more he eat, the fatter he'll get. The fatter he gats, the slower he will move and his jumps will be lower. If he eats too many burgers, he will have a heart attack and die. It's a neat novelty.
Okay, maybe those weren't so quick >_>.