Stop N' Swop

Stop N’ Swopping was a scrapped process for Nintendo 64 games developed by the company Rare in which you could swap one cartridge out and put another in in a relatively quick timespan in order to unlock rewards in the second game that was scrapped after newer Nintendo 64 models made it virtually impossible to complete. However, what many might not know is that Stop N’ Swopping games with Super Mario 64 can actually spread the Personalization A.I. to other games, resulting in all sorts of bizarre phenomena.

Backstory
Stop N’ Swop is most infamous for being a removed feature in Rare’s 3D platformer Banjo-Kazooie. The game was originally going to contain several eggs and a hidden Ice Key that could be used to unlock features in Banjo-Tooie and Donkey Kong 64 through a 10-second process in which the player would take the initial cartridge out of the console while it was still on and quickly putting in another cartridge containing a game that would then unlock rewards depending on the obtained items.

However, this process went unused as newer Nintendo 64 models were released that made this process virtually impossible due to the window of time being lessened to around 1 second, and Nintendo asked Rare to remove the feature as it may result in damage to the console. Despite multiple alternatives being available, the feature was removed, but fragments still remained as many players still found the now unobtainable and useless Ice Key in Banjo-Kazooie.

“Crossing Over”
Due to the process originally being designed by Rare, Super Mario 64 did not have any intended Stop N’ Swop features. However, due to the process by which Stop N’ Swop occurs, the data for the Personalization A.I. has been documented to be “carried over” to another game when Stop N’ Swopped. This can be applied to almost every known Nintendo 64 game, excluding the Nintendo 64DD, though it typically breaks the games it spreads to. The most common exceptions to this are 3D platformers due to their similarities to Super Mario 64, though other Nintendo 64 games such as Legend of Zelda: Ocarina of Time and other Mario games have also been reported to be potentially personalized.

The A.I. typically acts exactly the same as if it was in Super Mario 64, bringing back unused assets while creating new areas, though this sometimes conflicts with the game’s progression or even graphical consistency due to it being ported from a different game.

Legend of Zelda: Ocarina of Time
The most commonly seen example of the A.I. affecting Ocarina of Time is the addition of new areas, most commonly seen as the Sky Temple and Unicorn Fountain. However, other common rumors such as the Triforce, rumored tunics, the Sword Beam, and extra weapons have appeared. It is believed that most of the content added by the A.I. was recovered from what would have later become Ura Zelda if it ever came to fruition. One of the most notable anomalies the inclusion of a special type of Key Item to tie Ocarina of Time and Majora’s Mask together, being Majora’s Mask appearing in Ocarina of Time in one of the shops to unlock a playable Adult Link in Majora’s Mask.

Banjo-Kazooie
Banjo-Kazooie’s most common symptom of crossing over is the re-implementation of the Stop N’ Swop items initially intended, though they do not typically unlock the intended rewards in Banjo-Tooie and Donkey Kong 64 unless those games have also been effected. However, extra Jiggies, new enemies and new attacks can also appear in the game.

Mario Kart 64
The most common anomalies seen in an “infected” Mario Kart 64 is the re-implementation of the Magikoopa racer, the addition of the Pokey Oasis track, and the ability to unlock Marty the Thwomp, though the name and coloration is typically not actually present. New items, obstacles, and even a playable Waluigi have also been reported.

A rare promotional card for Mario Kart 64 featuring the playable cast notes that "[Luigi] missed his chance to be in Super Mario 64 because he was too busy tinkering with his kart", thus adding to the theory of connectivity between the two games, subtly hinting as a possible Stop 'N Swop bonus.

Paper Mario 64
Paper Mario 64 commonly reimplements unused badges and fights, such as the Albino Dinos and Whackas, as well as new partners, usually a fully functional Goompa & Twink, the re-implementation of Goombaria, or an entire new character. Notably, boss rematches are another common phenomenon, implying some development relevance of some kind.

Inverse Swapping
According to some who have accidentally Stop N’ Swopped with Super Mario 64 as the second game, the Personalization A.I. can use assets from the previous game and assimilate them into the game. This can also occur with games that have experienced crossing over. This commonly manifests as areas and landscapes from other games appearing as new courses, such as a temple level from Legend of Zelda: Ocarina of Time or Majora’s Mask appearing in Super Mario 64, or a new area of Princess Peach’s Castle resembling Hyrule Castle or one of the many temples.

Key Items
Main Article: Key Items

A common thread between reports of Stop N’ Swop with Super Mario 64, either after crossing over or inverse swapping, is that after it has occurred, the A.I. will begin implementing “Key Items” into Super Mario 64 that act in a similar manner to how the Ice Key and Stop N’ Swop eggs were to act in Banjo-Kazooie. For example, if one were to find Big Bully’s Key, this could be reinterpreted as an analog to the Ice Key and seemingly be intended to unlock a lava area in Banjo-Kazooie, though the A.I. is usually not consistent with this unless the attached game has experienced crossing over.

Key Items have also appeared in games with crossing over to attach to Super Mario 64 in some way, named “Inverse Items”. An example of an inverse item is the Ghoul Medal appearing in Paper Mario as a usable badge and can then be found in Super Mario 64, or unlock levels theme around Paper Mario locations such as Toad Town or Mario’s House.

Theorizing
The crossing over phenomenon appears to be the source of many playground rumors from the Nintendo 64 era, as many children who played the console when the older models were released could have potentially encountered the mythical areas such as the Sky Temple or Marty the Thwomp and then told their friends, causing the rumors to spread and distort to the modern state many know today.

Trivia

 * According to those in possession of them, the NINT can still perform Stop N’ Swop with a 30-second timeframe instead of the 10-second timeframe present in the primary console. This has led some to speculate that “damaging the console” was a cover-up for Nintendo discovering the crossing over phenomenon while developing the peripheral.