Hotel Mario is very similar in gameplay to Looney Tunes Hotel, a game planned for the Atari 5200 but cancelled. It's unknown whether Hotel Mario's development team actually knew of this game.
Similarly to With the Beatles, Hotel Mario holds the dubious and downright morbid distinction of having been released on the exact same day of the exact same year as Kurt Cobain's suicide.
Later, and by sheer coincidence, The Super Mario Bros. Movie would be released on the 29th anniversary of Hotel Mario's release.
Bury Your Art: The game has never been reissued in any way since it first came out, thanks to its negative reputation among not only fans and critics, but also Nintendo themselves, who refuse to acknowledge its existence.
Contractual Obligation Project: This game, along with the Zelda CD-i games, exists as part of a contract Nintendo and Philips made after the cancellation of the SNES CD-ROM. Consequently, Nintendo had little interest or oversight other than ensuring that the characters were on-model in the packaging and manual artwork.
Dummied Out: Although the game's only in-game "tutorial" is telling players to Read the Freaking Manual, there is an unused recording of Mario (apparently a temp track done by someone other than Marc Graue) instructing the players on the game's basic mechanics. This is still present in the released build's files, even though the corresponding gameplay footage present in the beta build was cut.
Keep Circulating the Tapes: The game is not available in any other platform, and given the CD-i's notoriety for being next-to-impossible to emulate properly, those who wish to play it will have to pay a lot of money just to get a copy (and even more for those who don't have a CD-i). Nintendo has made it clear this game never happened, so even if they somehow owned the rights, they would have no appetite to put it out on their Virtual Console platform or anywhere else.
Orphaned Reference: When instructing the player to "check out the enclosed instruction book" in the intro cutscene, Mario holds up one finger. This is a holdover of the cutscene's original dialogue, where he would have told players to press button 1 for instructions or button 2 to skip ahead to the game. The animation of him holding up two fingers was cut in the final version, which freezes on the frame of Mario holding up one finger.
This wasn't the only Mario game planned for the CD-i. Two more, Super Mario's Wacky Worlds (a CD-i exclusive successor to Super Mario World, and probably the most promising of all the CD-i Nintendo games, released or otherwise) and Mario Takes America (an educational game) were planned, but were cancelled due to a variety of issues. That said, the basic idea of Wacky Worlds, Mario traveling the world, was (unintentionally) revisited in Super Mario Odyssey, over two decades later.
Hotel 6 has no game data, with the internal level order skipping from 5 (Ludwig) to 7 (Wendy)note contrary to Urban Legend of Zelda, no, it cannot be unlocked by beating the game in under an hour — it just doesn't exist in there. This is further supported by Bowser's dialogue in the beta intro cutscene where Bowser mentions eight Koopa hotels instead of just seven. Accordingly, a "Cheese Hotel" was among one of the concept drawings, but development was disgusted by the idea and promptly had the artist sacked. Presumably, this would have belonged to Iggy, who doesn't have his own hotel in the final game.
, a game planned for the Atari 5200 but cancelled. It's unknown whether Hotel Mario's development team actually knew of this game.