Unintended Playable Characters

Unintended Playable Characters (UPCs) are characters in Super Mario 64, which due to either the Personalisation A.I. or alterations of the base code of the game via Gameshark and others like it, can be played as an unintentional feature in the game. The characters' playability and controls vary between copies of the game. Examples of characters can be playable unintentionally are Peach Bowser, Yoshi, Wario, Toad, different colors of Mario,  an enemy from the game, such as a koopa, and Luigi.

Analysis
In the base coding of the game, it is unintended for characters other than Mario to be playable through any means necessary. However, experiences with hacking and the personalization A.I allow unintended playable characters to function. Most reports of these playable characters' functionality seem to suggest that they control just like Mario himself, since his functionality as a playable character is the most common in the code. Such personalizations and coding can be found in videos demonstrating these codes and "blooper" videos regarding Super Mario 64.

Most of these playable characters seem to be unintended because of their programming seeming to not have the animations required for the control patterns of Mario. As such, distortions of the models of unintended playable characters are common throughout multiple copies of Super Mario 64. However, some reports do come out regarding of differing control styles of these playable characters. The most frequent alterations regard the speed, jump length, collision detection, and object interactions of these unintended playable characters. It seems to be a randomization factor that checks in sometimes when it comes to these playable characters.

Unlocking such characters varies from copy to copy, and the most frequent alleged methods of unlocking characters regard Luigi. This can be a result of many people's subconscious desire to unlock Luigi in the game, not unlike the Wario Apparition. The "L is real 2401" rumor is represented to be a clue in a large group of these rumors, as it seems to be a representation of Luigi in the game. Luigi's playability is reported to be the most stable, as he's merely an altered version of Mario. The desire for Luigi in the game and that there was originally 2 player functionality with him as the second playable character in Super Mario 64 could be two major factors on the stability of Luigi himself.

Theories
The purpose regarding the function of the unintended playable characters is unknown. One theory could be that this was meant for filling the slot for a second playable character long before Luigi was developed in the beta of Super Mario 64. Somehow, it seems to not be scrapped in the game's files, as it can be somewhat brought back through the AI and programs like Gameshark. Another theory would be that it was an unintended feature in the coding of the Personalization AI, as it seems to be embedding in most if not all of the coding of the game, which can include playable character functionality. Enabling and disabling of this feature could also be caused via The Self-Patching Anomaly trying to disable the mechanism, with varying results.

Luigi being the most stable and the most consistent in the list of Unintended Playable Characters, along with the original purposes of him in the game provide a certain skepticism regarding Nintendo's statements on Luigi not being playable in the game. This could be Nintendo trying to deny the Personalisation AI's existence, as more malicious parts of the coding are rumored to be a part of the game.

Trivia

 * The phenomenon on Unintended Playable Characters could be an inspiration for the playability of Luigi, Yoshi, and Wario in Super Mario 64 DS. This does not prove that the DS game is personalized, however.
 * The DS version would only be personalized if Nintendo decided to add the AI back, which would mean they would be lying about the AI.