Super Mario Disk Version aka "Super Mario 64DD" (found unreleased Nintendo 64DD port of 3D platformer; 1999)
In 1996, the first game for the Nintendo 64 console was released. The game was called Super Mario 64, and was the first 3D game in the ever popular Super Mario series of video games.
Production of the N64DD
A few years afterwards, Nintendo released an add-on to the Nintendo 64 called the Nintendo 64 Disk Drive or Nintendo 64DD for short. The add-on would have utilized magnetic disks instead of the standard game cartridges. It failed greatly, so it was never released outside of Japan. Because of this, several games and expansion packs in development for the 64DD were subsequently cancelled. One of those cancelled games was a sequel to Super Mario 64 simply titled Super Mario 64 2.
Super Mario 64 2 was to have the same graphics and style as its predecessor; the only other known information about it are the facts that Mario's brother Luigi was going to be a playable character, and that only one demo for the game was ever made (though this demo was never released to the public, nor has any footage of said demo ever surfaced). In 2004, the remake of Super Mario 64 titled Super Mario 64 DS was released for the Nintendo DS, and took several traits from Super Mario 64 2, including playing as different characters like Luigi.
UPDATE: July 2014: In June of 2014, a demo of a 64DD version of Super Mario 64 surfaced, However it is not a full sequel as the rumors had stated, But appears to be an improved version of the original release with better textures, Music and Loading times.
The demo is very buggy and goes to a black screen at seemingly random times, It's unknown whether this is due to the alpha nature of the game or data rot.