Super Mario 64 (Nintendo 64DD)

Super Mario 64 was originally going to be ported and updated for the Nintendo 64DD, a disk drive addon for the Nintendo 64. The game was showcased at the Shoshinkai 1996 show. However, with the addon's failure the Nintendo 64DD version of Super Mario 64 never saw the light of day.

A version of the game was found, featuring a slightly altered castle theme and a few other alterations.

Reportings

 * Everything in this section should be taken with a grain of salt. These are all unverified claims.

Fourth Floor
On 4chan, an unverified claim was put onto /v/ back in 2006. This was coinciding with the release of New Super Mario Bros. on a discussion about Super Mario 64 DS. The veracity of this post is uncertain, with the posts unarchived and no photographical evidence of this ever happening.

An anonymous user claimed to own a disk with "SM64" haphazardly scribbled onto it. One user suggested that this is the elusive Nintendo 64DD version of the game, and the user got to asking one of their abroad friends to see if they could snag a Nintendo 64DD from anywhere. Fortunately they could, and were able to play the game.

Most of the documentation of what happened in the game has been lost, but apparently the user ended up beating the game. After beating the game, apparently a fourth floor would open up for the player to access. This fourth floor apparently housed new levels which were very difficult. The contents of these levels has been lost to time, but it's known that the player had to fight a floating Wario head (bearing resemblence to the Wario Apparition) at some point.

If there is any other information about this anonymous user's gameplay, it should be put here.