StarPass

The StarPass, also known as "Project StarGate", is an unreleased application for the Nintendo DS. It would allow you to link 2 compatible games and unlock extra content in both games. The most famous use of the StarPass was to unlock Waluigi in Super Mario 64 DS by linking the game with the similarly cancelled Wow! Waluigi, though there were several other compatible games planned. It was cancelled when it was found out that the Personalization A.I. of SM64DS spreads to other games it was linked with, causing said infected games to become incredibly unstable and nearly unplayable.

Description
There were 3 planned ways to use the StarPass application. You could link 2 digitally downloaded games simply by selecting them in a pop-up menu, having a game cartridge inserted into the DS and selecting a single digital game, or using a unique add-on to link together 2 cartridges by inserting them into the 2 slots on the peripheral and then inserting it where cartridges normally go. Once the 2 games are selected, the StarPass will check if they are a compatible match, and if they are, the StarPass would unlock the applicable data in both games.

The StarPass' app icon was a simple image of a Power Star, potentially as a placeholder for a later icon that would have been made if it was released. The GUI was more complex, however, having a checkered background similar to that of the anomalous Star World level's painting, being cyan and blue checkers with several star silhouettes along them. Whether or not this is a coincidence is unknown.

Known Combinations
''This is a list of all known combinations associated with StarPass, and their effects. Notably, these extend to several years after it's cancellation, implying it may have had a resurgence planned at some point before ultimately being scrapped again. If any more combinations are discovered, they are to be documented in this page and anywhere else it'd be applicable.''


 * Wow! Waluigi & Super Mario 64 DS: The most famous use of StarPass, linking these 2 games would unlock the levels associated with Waluigi in Super Mario 64 DS, specifically the Negative World and Piranha Pit, though other levels such as Rabbit Meadow may have also been unlocked. Notably, data found indicates that it would also somehow affect Waluigi Mode, but how is unknown. In Wow! Waluigi, it unlocked Warupichi as a playable character, as well as an unfinished level based off of Super Mario 64 DS.
 * Mario Kart DS & Wow! Waluigi: In Mario Kart DS, a unique track named Dazzling Desert is unlocked, being a desert made out of diamond dust, likely as a reference to the Dazzling Diamonds. No known associated reward in Wow! Waluigi exists, but it may be tied to the unused desert level found in W!W's files due to Dazzling Desert sharing the same theme.
 * Super Princess Peach & Wow! Waluigi: In Super Princess Peach, Warupichi can be unlocked as a playable character by using the StarPass with Wow! Waluigi. However, they are highly unfinished, and only appear to be a reskin of Princess Peach. In Wow! Waluigi, Princess Peach is unlocked as a playable character, sharing all their abilities with Warupichi, but the StarPass also unlocks a unique level based off of Princess Peach's Castle you can only play as Princess Peach. This explains the unused Princess Peach textures found in Warupichi's files in W!W.
 * New Super Mario Bros. & Super Mario 64 DS: In New Super Mario Bros., some of Super Mario 64 DS' minigames would be unlocked in-game, as well as vice versa for Super Mario 64 DS. More may have been planned, as this is clearly the most lackluster of all StarPass usages.
 * Mario Party DS & Wow! Waluigi: In Mario Party DS, Waluigi's Island from Mario Party 3 is unlocked as an extra stage, alongside several new minigames. In Wow! Waluigi, Waluigi's Island is unlocked as a playable level.
 * Yoshi's Island DS & Wow! Waluigi: In Yoshi's Island DS, Baby Waluigi is unlocked in an extra world. Baby Waluigi does not have a special ability however, likely due to being unfinished, meaning the levels cannot be cleared without hacking the game. In Wow! Waluigi, an unlockable purple Yoshi mount nicknamed Wa-Yoshi by the community can be unlocked that has faster speed, Yoshi's flutter jump and can even eat enemies to create eggs.
 * Animal Crossing: Wild World & Super Mario 64 DS: In Animal Crossing: Wild World, a new classic Mario Bros. game is unlocked. In Super Mario 64 DS, a new level based off of Animal Crossing is unlocked, with a single mission requiring the player to collect 5 Silver Stars.
 * Kirby: Squeak Squad & Super Mario 64 DS: In Kirby: Squeak Squad, the Smash Copy Ability from Kirby & The Amazing Mirror is unlocked as a usable ability. In Super Mario 64 DS, a new mini-level is unlocked based off of Kirby's world with a single Power Star the player has to platform towards.
 * WarioWare: Touched! & Wow! Waluigi: In WarioWare: Touched!, a new set of minigames tied to Waluigi would have been unlocked. In Wow! Waluigi, Wario-Man would be unlocked as a playable character, being an upgraded version of Wario with advanced versions of Wario's abilities.
 * New Super Mario Bros. DS & Wow! Waluigi: In New Super Mario Bros. DS, an extra world is unlocked with a collection of themes of levels from Wow! Waluigi, similarly to NSMB Wii's World 9 being a collection of themes from throughout the game. In Wow! Waluigi, an extra cloud level named Soaring Skies is unlocked, with the Lakithunder boss fight from NSMB.
 * Sonic Rush & Sonic Rush Adventure: A rare third-party example, it seems that StarPass's resemblence to the "lock-on" feature of Sonic & Knuckles was not lost on Sega themselves. Thus, linking these two games results in the StarPass app booting the system into an outright combination of the two games. In true lock-on fashion, the earlier game is played first, and then upon beating it, the story will transition smoothly into the later game's content.

Cancellation & Rediscovery
Despite never being publicly unveiled, the StarPass was hinted at at E3 2004 when Wow! Waluigi was unveiled alongside Nintendo DS and advertised as "revolutionizing the game industry." Around 2013, a group of teenagers explored the house of a former Nintendo employee, discovered Wow! Waluigi, as well as the physical peripheral for the StarPass, and documents that explained why the StarPass and Wow! Waluigi were cancelled. When Super Mario 64 DS is linked to a game, through unknown means, the Personalization A.I. spreads to the other game, making it potentially unplayable. Nintendo then cancelled StarPass to avoid this issue, as there would likely be numerous complaints, and they wanted to keep the Personalization A.I. out of the public eye. Wow! Waluigi was made for StarPass to unlock Waluigi in Super Mario 64 DS, so it was cancelled as it's purpose couldn't be fulfilled.

Theorizing
Despite StarPass being canned before the release of the Nintendo DS, numerous games that weren't launch titles and came out years later appear to have StarPass-related unused content. It is possible that some of this data isn't actually related, but the leading theory is that StarPass' cancellation wasn't announced to the developers of these games for a long time, meaning that they still added StarPass compatibility only to realize that it was never released. Considering the reason StarPass was cancelled and the A.I.'s confidentiality, this may be the case, especially when factoring in that Nintendo silently cancelling things and not explaining why has occurred before.