The Legend of Luigi in Super Mario 64
Over 25 years after the original release of Super Mario 64, a fan has uploaded some old footage online that showed that Luigi was planned to be playable in the game before being cut during development. Luigi being in the original Super Mario 64 was one of the biggest and longest standing gaming urban legends. Despite the theories and legends was ultimately dismissed as a rumor.
Luigi Mario 64 screenshot
In 2020, there was the infamous Nintendo gigaleak, which dumped a ton of information and source code from older Nintendo games, including an early build of Super Mario 64. Dataminers who dug into the source code found evidence of Luigi being in Super Mario 64. What was found was almost completed too, such as textures and a model that would have turned Mario into Luigi, though the implementation of a playable Luigi was not completed in time. Recently, some footage has been uploaded that further shine a light on Luigi's planned inclusion as a playable character.
The Rare Footage
The footage was uploaded to YouTube by Now In Game Channel, which contains rare VHS footage of Nintendo's 1995 Japanese Space World Show. This was where the Nintendo 64 console was showcased for the first time. Around the 13:21 mark of the video, eagle-eyed viewers can spot to the right a build of Super Mario 64, with Luigi jumping towards the screen. It's only on-screen for a few seconds, meaning it is very easy to miss.
If this footage is to be believed, this would make it the first time Luigi has been seen in Super Mario 64 outside the massive Nintendo gigaleak from 2020. An old interview from a Nintendo strategy guide (archived by VGC) has Shigeru Miyamoto describing the process of designing the game, creating rooms made of 'LEGO-like blocks' that allowed Mario and Luigi to jump, run around, and more. This description seemingly matches the video footage provided by Now In Game Channel.
The Scrapped Multiplayer Mode
According to Miyamoto, Luigi was included as a playable character in a scrapped multiplayer mode for Super Mario 64. Due to a combination of memory issues and the likelihood that players would only have one controller when Super Mario 64 was released, Luigi was left out of the final build of the game. The closest Luigi would come to being playable in Super Mario 64 would be in the Super Mario 64 DS remake.