Top: In Super Mario Galaxy 2, there is a room inside Starship Mario that contains pedestals that display power-ups Mario has obtained during the game. However, the Spin Drill is slightly too large to fit into the display case, so it is resized to be smaller. During the brief iris-in screen transition when Mario enters the room, the Spin Drill is its usual size, and can be seen overlapping the display case.

Bottom: Moving the camera allows us to see this happening up close. The drill shrinks on the frame the screen transition ends.
_{Main Blog | Twitter | Patreon | Source: SMG2 in Wii emulator, special thanks to twitter user “HEYimHeroic”}

Characters highly resembling Mario and Luigi appearing in a short segment in the Foster’s Home for Imaginary Friends cartoon. They are carrying a frame and become angry at another character for breaking the glass in it, hitting him.
_{Main Blog | Twitter | Patreon | Store | Small Findings | Source}

The file size of the Super Mario Sunshine disc is 1,425,760 KB or 1.35 gigabytes. The video files used for the game’s prerendered cutscenes, such as Mario’s trial and imprisonment at the beginning of the game, are saved as .thp files in the file system.

Extracting all the video files and adding their sizes together gives us 874,588 KB, or 834 megabytes. This means that 61.34%, or almost two thirds, of the disc is taken up by the cutscenes.
_{Main Blog | Twitter | Patreon | Store | Source: myself, data extracted from Super Mario Sunshine (NA, GC)}

Top: Official artwork released by Nintendo for Dr. Mario on the NES. The artwork is cut off; this version of it has for a long time been assumed to be the only version, with no uncropped full drawing existing.

Middle: A 1995 manga discusses what the full image could have looked like, noting the discrepancy between Dr. Mario’s and Nurse Peach’s heights in the image compared to their usual heights and hypothesizing that one of the characters’ legs would need to be the wrong length.

Bottom: Twitter.com user “sayokoskatti“ has discovered a full version of the artwork in an obscure information brochure for proper care and cleaning of the Nintendo Famicom Disk System. While Dr. Mario appears to be sitting on a stool here, explaining the inconsistent heights, looking closely at the original cropped artwork, he is depicted standing instead.

Since the full version does not entirely match the cropped version, there is no clear solution to the discrepancy. Should additional versions of the artwork surface, I will post updates on the situation.
_{Main Blog | Twitter | Patreon | Store | Sources: 1, 2: see bottom of image, 3}

Mario Kart: Double Dash contains a hidden functionality that provides a code after a Time Trial race that includes information about the track, the characters and kart used, as well as the total time and the fastest lap time.

If, after completing a race, the buttons L, R, L, R, X, Y, X, Y, Z are pressed in that order on the retry menu screen, the unique code will appear (top right). A player-made decoder is available online here (bottom); inputting the combination will correctly decode information about the race (compare with the times displayed at the end of the race, top left).

Unfortunately, this functionality was never used outside of a single contest by Nintendo exclusive to Japan, although it is available in all versions of the game.
_{Main Blog | Twitter | Patreon | Store | Source: myself, Mario Kart:Double Dash (NA, GC) in GC emulator}

In a piece of official artwork for New Super Mario Bros. Wii, the lowest spine on the back of Yoshi’s head is missing. It is most likely removed so it does not clip into the Yoshi’s back. The spine is not merely hidden by the Yoshi’s body; the bottom image is an animation of a different Yoshi render being overlaid over the artwork, showing that the lowest spine should have been visible in the gap between the head and the body if it was present.

This is not the only time New Super Mario Bros. Wii adjusts Yoshi’s model for aesthetic reasons; some artwork also shifts his saddle around on his body, as shown here.
_{Main Blog | Twitter | Patreon | Store | Small Findings | Source 1, 2}