Mario's Castle

Mario's Castle was supposed to be a video game for the scrapped Project Atlantis handheld; the premier video game that would make it sell. The game itself would be scrapped alongside the handheld due to the latter's failings when it came to Nintendo's standards.

The only mention of the game was from a 1996 issue of the Electronic Gaming Monthly magazine, and the only information regarding the game was that it was going to be developed by Nintendo of Japan. As such, speculation has ran rampant when it came to what the game would contain. The most likely guess on what the game could be would be that it was meant to be connected with Super Mario 64, considering that Project Atlantis was originally going to have a link port (most likely for the Nintendo 64).

Mario's Castle could be a reference to the Super Mario Land games, specifically Super Mario Land 2: Six Golden Coins where Mario had a castle that Wario took over. As such, it could be assumed that the game itself was a platformer, most likely a 2D one.

Personalisation
Considering what has been known about Super Mario 64; that every copy of the game is personalized, it could be reasonable to assume that once Mario's Castle had been linked to Super Mario 64, the personalization AI would be linked to the game. This personalization could be for finding bonus stuff in both games and adding newer content that could be utilized for the game.

However, the unpredictable nature of the AI could have been a major result on why the idea for Mario's Castle would be scrapped, as it could have lead to corruptions of the game itself. Transferring the AI from the Nintendo 64 to Project Atlantis could provide these corruptions because of the different coding for the systems. This can also be a reason why the game itself was referenced only once; it was a dud that was a part of the dark rabbit hole of Super Mario 64's underbelly.