2001
In Super Mario 64, only half of a Lakitu's model is displayed when Mario is far enough away; however, which half depends on whether Mario has already approached the Lakitu. If Mario did not yet approach it, only the Lakitu's body is loaded, if he did, only the cloud is loaded.
2002
The area lighting specifications in the data of Super Mario Galaxy were never updated if an area was deleted, leading to the lighting file containing names of 34 deleted zones and galaxies. Some, like "ChristmasBattleZone", do not resemble anything found in the finished game.
2003
Top: official artwork of Mario's mustache without his nose, released by Nintendo of Japan for Super Mario Odyssey. We can see that while most of the mustache has a more realistic texture, the middle, normally covered up by the nose, has a different, more stylized texture.
2004
Yoshi's unobscured overworld sprites from Super Mario World/Super Mario Advance 2. These can normally never be seen in-game as Mario or Luigi are always riding Yoshi and partially covering him, but are actually saved separately from Mario and Luigi's sprites in the data.
2005
In Mario & Luigi: Superstar Saga, walking against the plant in this corner of the Hoohoo Village cave (top left) with Mario in front will make Mario seemingly disappear (top right). However, Mario is simply teleported very high up and will fall down after a while (bottom).
2006
Mario and Luigi: Bowser's Inside Story contains a debug menu, accessible by modifying the game's code. In the Japanese version (left), all entries in the menu are individually labeled. The North American version (right) translates all of them with "no need to translate".
2007
Mario Party 4 contains a debug "model test" room that contains only Mario, ten Whomps, and a ring of flames (top). Once the room is loaded, all buttons only make mini-game ending messages appear (bottom). It is impossible to exit the room.
2008
The "Special Episode" DLC for the Nintendo Switch version of Captain Toad: Treasure Tracker contains new, unique illustrations used in the book menu between levels, as in the base game. However, the data for the DLC also contains these two illustrations that are not used.
2009
In Mario Kart Wii, resetting the Team Race menu until you are on the blue team, then exiting and choosing Solo Race will make the Fake Item Boxes dispensed by your character blue despite there not being a blue team in a Solo Race.
2010
The cover of "Mario and the Incredible Rescue", a licensed Mario book, contains 5 pieces of artwork from 4 games: Mario and a 1-Up Mushroom from Super Mario 64, Luigi from Super Mario 64 DS, and two Boos from Mario Kart 64 and Luigi's Mansion, respectively.
2011
Thanks to the quick efforts of my readers, Goombo has been found! Special thanks to @ultra_jawbone for the first picture, as well as @JackalFrost, @thursdaysrain, @conorsuks and everyone else who contributed a picture! I am so grateful for your cooperation! Goombo is confirmed!
2012
"Magnet Mario", one of the winners of a "design a Mario power-up" contest held by the British Computer and Video Games magazine.
2013
While the microgames in WarioWare, Inc.: Mega Microgames can only be played in three difficulty levels, there is functionality in the code supporting even higher difficulties. Setting the level over 3 in "The Brush Off" results in the teeth cycling through colors of the rainbow.
2014
Concept art for Super Mario 64 featured in the Super Mario Bros. 25th Anniversary Collection booklet (left) shows that the team envisioned Mario to be able to swing on horizontal bars in that game. The idea went unused; however, it was implemented in Super Mario Sunshine (right).
2015
Mario Party 2 contains a debug model test accessible by modifying the game's code. In it, we can see that the texture of Cowboy Wario's eyes is stretched further vertically compared to all his other forms, giving him a more surprised or shocked appearance.
2016
Paper Mario sticker from Metroid Prime 3: Corruption, unlocked as a decoration for Samus's Gunship by having the game detect a Wii save file for Super Paper Mario on the system.
2017
The unreleased "Donkey Kong's Music Play" for the Famicom, shown in a 1983 Nintendo promotional handout. This screenshot shows the "Donkey Band" Karaoke mode.
2018
Bowser confronts Mario, Luigi and Yoshi in a Super Mario 64 manga.
2019
Unique official artwork of penguins seen in a wallpaper provided on Nintendo of America's former site for Mario Kart: Super Circuit.
2020
Stained glass window depicting Wario, seen in the final rounds of the Hard difficulty of the Vs. Com mode in the SNES version of Wario's Woods.
2021
All color schemes of Referee Mario from Mario Tennis for the Nintendo 64, viewed in the in-game debug mode. Referee Mario never wears his blue hat with his green jacket.
2022
In the data of Super Mario Sunshine, an early beta screenshot can be found that shows a large island with a tower next to Ricco Harbor that is completely absent from the finished game. This may be "Warship Island", a deleted level that appears on an internal level name list.
2023
The early beta build of Super Mario 64 playable at the 1995 Japanese Shoshinkai trade show featured a minimap of the course displayed in the top right corner of the screen. While scrapped in the finished version, the minimap was included in the remake, Super Mario 64 DS.
2024
The 1989 licensed Nintendo Sticker Activity Book included stickers of a variety of Super Mario Bros. and Super Mario Bros. 2 characters, some featuring original artwork. As part of a puzzle activity, the letters in the names of all characters on the stickers have been scrambled.
2025
Artwork of Tanooki Mario from a licensed Argentinian Super Mario Bros. sticker book.
Additional obscure Mario content for suppermariobroth.com.
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