On September 26, 1996 in North America, Nintendo released Super Mario 64, the Nintendo 64 launch title and also the first 3D installment in the Super Mario franchise. A few years afterwards, they released an N64 add-on called the Nintendo 64 Disk Drive (or Nintendo 64DD for short). This would have utilized magnetic disks instead of the standard game cartridges. Due to the 64DD's great failure (having only been released in Japan), several games and expansion packs in development were subsequently cancelled. One of these abandoned games was a sequel 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). On November 21, 2004, a 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. Yoshi was playable, so is Luigi and Wario. The player first plays as Yoshi, with Mario, Luigi, and Wario being unlockable characters. Also in these games, there were rumors of Waluigi appearing in it.
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.