The "Eclipse" demo that convinced Nintendo to focus on 3D gaming has been discovered
Back in 1992, Nintendo released a 3D game exclusively in Japan for the Game Boy titled simply "X", which precedes any other 3D game from Nintendo. However, "X" was but the implemented of a previously showcased demo to Nintendo, which enticed them to delve deeper into the 3rd dimension for their own games.
Dylan Cuthbert, a programmer hired by Argonaut Software at the young age of 17, showed special expertise on programming for 8-bit systems at the time, and his interest for the Game Boy is what presented the inception for the 3D work on the system by Cuthbert. Argonaut initially didn't have an official Game Boy devkit, so they instead took an already existing cartridge for the Game Boy, opened it up and effectively hacked the cartridge by rewiring it with their Amiga computer to allow for their own addresses bus and ROM to be loaded instead of the cartridge's.
Once the work on the base cartridge was made by Argonaut, it was up to Cuthbert to develop a 3D engine for the system and prepare a demo of it running on a Game Boy with the tentative title of "Eclipse". Cuthbert eventually managed to get the 3D engine to work quite well on the system, and the demo he developed was a combination of a first person tank game, similar to that of Battletank on the NES, and the second which was a fly-through 3D game in which the player evaded obstacles, serving as a special level in-between the main tank stages. Additionally, the ROM also contained an object viewer, which let the player visualize, rotate and scale the 3D objects from the game.
It was during the time in Mindscape's hands that the demo itself would end up in the hands of the current owner, Michelle Flitman (daughter of Mindscape's producer at the time, Mark Flitman), who reached out to the Video Game History Foundation. Initially, Michelle didn't know about the existence of this specific demo, only reaching out to the VGHF based on a number of pre-release game cartridges, tapes and other documentation, and it wasn't until they went through the various contents that Mark had on his home that they bumped into the elusive "Eclipse" demo.
The creation of the "Eclipse" demo, and the subsequent release of its fully-fledged release known as "X" (or Lunar Chase), essentially sparked the interest for Nintendo shift its focus on 3D gaming, spawning the creation of one of Nintendo's top IPs to this day, Star Fox, which saw its first release on the Super Nintendo just a few years after. The rest is history, as Nintendo then continued their work on 3D games after Star Fox to what would become their Ultra 64 project... Becoming what is now known as the Nintendo 64 and its whole slew of 3D classics.
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