Grazer-Razor!

Original 3D animation from a 1994 Hong Kong commercial for the Game Boy, promoting Super Mario Land 2.

While it features various characters like the Buzzy Beetle-like Noko Bombette enemy and the Bomubomu pig enemy from that game, some characters are included here who do not appear in that game at all like Luigi and Toads.

Note also that the yellow flying enemies are, extremely bizarrely, multiple copies of the Sewer Rat boss of Macro Zone. In-game, the Sewer Rat is a unique character, and being a rat, cannot actually fly. It does climb up walls and drop down, which the artists for the commercial may have interpreted as the ability to fly freely.

Source: magikarpfan77

Top: in World 8-4 in Super Mario Bros., there is an underwater section in a castle, the only one of its kind anywhere in the game. Normally, the player would simply emerge from the entrance pipe and continue to the right. However, if the player attempts to interact with the pipe, Mario will become hurt or even killed by something seemingly invisible.

Bottom: if Mario is Fire Mario, shooting a fireball at the pipe will also destroy the invisible object and award 200 points.

This is actually a Piranha Plant which is invisible due to being incorrectly drawn behind the water background instead of in front of it. The reason the Piranha Plant is there to begin with is because every single upright pipe in the game that is not in World 1-1 is programmed to spawn a Piranha Plant if there are enough object slots open (not too many other enemies are already loaded).

This results in some pipes appearing to not have Piranha Plants during regular gameplay (as they are usually reached when there are already too many other enemies loaded), but even they can be made to spawn Piranha Plants if Mario systematically defeats and unloads all enemies around them. This invisible Piranha Plant is simply a combination of this implementation and a graphical oversight.

Collection of all types of items retrievable from dedicated Yoshi's Island claw machines, available in Japan in 1996. Note that the two Baby Marios have different expressions and arm poses.

Source: blacktangent

In Super Mario Galaxy 2, crouching at the edge of a mud puddle will cause Mario (or Yoshi) to walk if the crouch button is continued to be held, although still at crouching speed (internally, he is in the crouching state, merely with a walking animation).

This results in "phantom mud" where Mario appears to be stepping into invisible mud even on clean surfaces as long as the button is held.

Source: SPG64

i see nothing explicit here...

except maybe this pop star but that is typical for celebrity attire unfortunately

In Mario Kart: Double Dash, the place where the drivers emerge from after going inside the Warp Pipe on the Peach Beach track is supposed to be an open window above the pipe (the only open window on the track, making it clear this was the design intent), but this is nearly impossible to see in-game.

Top: the closest this can be seen is in two-player mode if one player turns around to look at the building, but the game's camera does not move up high enough to show the window unless the second player is very far away. As such, this is basically not visible (note Mario and Luigi being barely larger than a pixel on Wario and Waluigi's screen). Also note that this game does not have a rear view button so Mario and Luigi cannot look behind them as they would be able to in later games.

Bottom: only with external tools can the camera be shifted in such a way as to actually show what is happening. Note that the window is aligned with the Item Boxes but not with the exit point of the drivers; this is possibly a remnant from earlier in development where the arc was different so that the drivers could emerge directly from the window and grab the Item Boxes.

Source: Peardian

Top: artwork used on a rare officially licensed 1986 Famicom game case, depicting the cast of Super Mario Bros. riding a car.

Bottom left: this artwork would later be used for the album cover of a 1986 Super Mario Bros. Japan-only vinyl record.

Bottom right: the place this artwork was most famously used was the cover of All Night Nippon: Super Mario Bros., a limited-edition retool of Super Mario Bros.: The Lost Levels for the Famicom Disk System that replaced some characters with caricatures of Japanese radio personalities.

With the bottom two in mind, looking at the top image reveals that due to their format, they have been cropping out details of the original drawing all along. In particular, the smiling sun on the left, the full fortress on the right, and most notably the Spiny riding a Lakitu's Cloud in the top right can not be seen in any of the later versions.

Spinies have never actually been able to ride Lakitu's Clouds until Super Mario Maker in 2015, 29 years after this image was drawn.

Source: bigafrodogg