Niko (on Tumblr)

Comparison between the model for the cage containing the entrance to Big Boo's Haunt between Super Mario 64 (left side) and Super Mario 64 DS (right side).

In both cases, the two buildings inside the cage are actually modeled, which is extremely difficult to see in the games (particularly for the shed), but the way in which they are modeled differs between the versions. The Super Mario 64 version has less details but more authentic textures, while the Super Mario 64 DS version adds windows to the mansion but makes the buildings look much more primitive.

Source: MrGameAndSketch, Peardian

Players of Super Mario Advance may recall that one of the major changes in that game compared to the Super Mario All-Stars version of Super Mario Bros. 2 (on which it is mostly based) is the inclusion of two new boss intros for Fryguy and Clawgrip, respectively.

In both cases, the action stops and a cutscene shows four bubbles (identical to Wart's bubble attack) float up from the bottom of the screen and surround an entity before transforming it into the boss (a mask for Fryguy and a small Sidestepper crab for Clawgrip).

The game actually contains two unused scenes for the same intro happening with two more bosses: Mouser and Tryclyde, shown restored in the footage. Mouser is created from a unique small mouse sprite, while Tryclyde is created from a Cobrat.

This implies that during the game's development the idea of Wart's magic being responsible for most of the game's bosses was more prevalent, before these scenes were scrapped for an unknown reason.

Source: AkiraTheGamer

Pedestrian traffic lights

Really Big Coin Skrekkøgle

This is our Really Big Coin. It is big because it makes other things look small when photographed next to it. Actually, it is a 20:1 replica of the EUR 50-cent, you see it being milled out here. We needed to do quite a bit of sanding, lacquering and smudging to obtain the desired look and some climbing to get into required shooting position (you need to get up real high to take good pictures). The result is a short series of photographs, attempting to visually scale down real-sized objects.

Officially licensed 1986 Super Mario Bros. scratch-off game featuring original illustrations, from Japan.

Source: j-vintage-toys

Design from an officially licensed Super Mario Bros. T-shirt, featuring an original illustration of Mario skateboarding.

In Super Mario World, defeating a Galoomba (left) (known as Goombas at the time of the game's release) or a Koopa Troopa (right) with Cape Mario's diving attack will display a small unintended graphic that is very easy to miss due to how small it is.

These graphics are actually the game attempting to display a dedicated "squished Galoomba" or "squished Koopa Troopa" sprite, which existed at one point during development but were later overwritten by other, unrelated graphics that happen to be small enough to be easily overlooked.

The bottom image shows the sprites as they once existed, recovered from development files.