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In Super Mario Land 2, the file select screen shows the amount of levels completed on that file. Using a glitch, it is possible to make it display a number higher than the amount of levels in the game (the game has 32 levels; note 44 being shown in the footage).

For this, the player must play through a level that has not yet been completed on that file and activate the bonus minigame. In it, Mario has to obtain a prize, and then the game has to be reset just as he is leaving the room.

If the reset is done with the proper timing, the number on the save file will increase without the game registering that the level was completed, allowing this to be performed arbitrarily many times, adding 1 to the counter every time. However, if the counter reaches 99, adding one more causes it to roll back to 0 again.

The E3 2009 demo for New Super Mario Bros. Wii featured a different design for the power-up that granted the Propeller Suit form. Instead of the Propeller Mushroom seen in the finished game, it was simply the letter P with a propeller, likely referencing various P items in the Mario series like the P-Wing, P-Switch, P-Balloon etc.

In New Super Mario Bros. U, there is a hidden X in the wall before the secret exit in level 4-Ghost House. While present on a background graphical layer, it is covered up in-game by a decorative grass tile extending to the left from the lower platform. It is unknown if this was merely a marker for the developers or was intended to have some actual relevance to the gameplay.

In Mario Kart Wii, several battle courses have a hidden modifier that adds extra height to item throws.

The footage compares regular banana throw height on Funky Stadium with slight additional height on Block Plaza (also added on GCN Cookie Land) and even greater additional height added on GBA Battle Course 3 (also added on SNES Battle Course 4). The four courses mentioned here are the only ones that modify the height.

Unused switch highly resembling the Wing Cap Switch from Super Mario 64, found in the files of Super Mario Galaxy.

While this is purely speculative, the Red Star power-up is similar to the Wing Cap in functionality and is also associated with the color red; thus, it is possible that it was intended to be unlocked using this switch at some point as a nostalgic reference.