Mario's Castle (unreleased Mario game on GameBoy Atlantis prototype)

In 1996, Electronic Gaming Monthly magazine wrote about a title called Mario's Castle, which was supposedly going to be a launch title for Nintendo's GameBoy Advance prototype, the GameBoy Atlantis (which is an entirely different story altogether). Not much else is known about the game besides its name and that it was going to be a launch title for the GameBoy Atlantis.

YouTuber LSuperSonicQ made a video on the topic, discussing the Atlantis and Mario's Castle.