Play as Mario
First, beat the game 300 times in 1 month. Then, as an adult, play a song, any side. Keep playing it, until a Stachild rises out of the ground, annoyed, and yells, "Hey! Stop playing that stupid song! Some of us are trying to get some sleep here!" and he'll go back into the ground. Play your song once more, and you'll hear him say, "That's it, I can't take this anymore..." and rise out of the ground to fight you. He's easy to beat: just hit him a couple times with the Master sword. However, if you kill him, he's gone for good and thus will make it impossible to complete this cheat. Instead, let him defeat you. Once Link's dead, a message comes on screen to notify you that Link is permanently dead, and to play on another file. Turn off the N64 and remove the OoT cartridge. Then, grab your Super Mario 64 cartridge and a hammer. Take the Zelda cartridge and lay it on top of the Mario cartridge, then repeatedly bash the cartridges with a hammer until their circuitry fuses together to make a new cartridge. Take this new cartridge and put it into the N64. Turn on the game and go to the file select screen. You'll notice the file that Link died on will have all of it's files erased and is re-named "Mario". Congratulations! Your now start off in the kokiri village as Mario! Granted, after 5 seconds of playing as Mario, the game will freeze, so enjoy those 5 seconds! This cheat can also be done in Majora's Mask.