The sleeping fish enemy, known as "Rip Van Fish", will typically chase down Mario upon being woken up. However, if Mario is under the effect of a star power-up, Rip Van Fish will make an effort to flee in the opposite direction of Mario instead.

The grassy pond located half way up "Kappa Mountain", found near the start of the game on Yoshi's Island, is named after the mythological "Kappa" from Japanese folklore, which is often depicted with a small pool of water on its head. The name "Kappa Mountain" only appears in the game's instruction manual.

If you play the last level of the special world in the Japanese version of the game, at the very end of the level a lot of coins will spell out "YOU ARE SUPER PLAYER !!". To fix any grammatical issues, the international version changed this to spell out "YOU ARE A SUPER PLAYER !!".

In the Japanese version, Reznor's name is Bui Bui which is labeled on the wooden planks when you battle them in the fortresses. Bui Bui's name was changed to Reznor when the game was localized.

According to former Nintendo of America localizer Dayvv Brooks, the Reznors fought at the end of Fortresses were named after Trent Reznor from the industrial rock band Nine Inch Nails, similar to how he named the Koopalings after famous musicians.

In an early prototype of the game, the clouds in the sky are reminiscent of old Japanese art. The world it overlooks is a mushroom shape, which resembles the prototype overworld. It would later appear in the Super Mario Advance version of the game.

An unused 5-up logo can be found in the game's data. When used in game, the logo doesn't show up correctly. You can get a 5-up by bouncing on Wigglers, or by using a Game Genie code. It's fully coded, but the actual way the graphics are displayed is incorrect, as their properties are pulled from the code after the table with the score palettes. The 8x8 tiles used are incorrectly flipped horizontally and vertically.

When the original Super Mario World game was released, Luigi was a recolored copy of Mario. In Super Mario All-Stars + Super Mario World, Luigi's sprites were redesigned to look different to distinguish the two.

The game's ending shows Mario and Luigi with red and green shoes, despite the cover depicting Mario with brown shoes. Also, both Mario and Luigi wear brown shoes during game play.

Early screenshots of the game show that Raccoon Mario was to return, before being replaced by Cape Mario. A raccoon leaf and a few Raccoon Mario sprites are also present among other early Super Mario World graphics found within the data of a SNES test cartridge, used by Nintendo to test and diagnose the consoles and controllers.

The stage which is shown at the title screen is an unfinished version of the Special World level "Groovy".

Super Mario World was originally announced in 1988 as "Super Mario Bros. 4" in an interview with Nintendo president Hiroshi Yamauchi regarding the development of the Super Famicom. Not only was this over two years prior to the game's release, it was also announced two months prior to the Japanese release of its predecessor, Super Mario Bros. 3. While the game would receive the name Super Mario World when it was first previewed in July 1989, Super Mario Bros. 4 was still used as a subtitle in the game's Japanese promotional materials, box art and cartridge label. The subtitle was planned to be used on the title screen for the game, as there is an unused graphic for it in the game's ROM. Some commercials for the game used either that subtitle, or just "Super Mario Bros." instead. In all versions of the final game however, neither of these subtitles were used.

The game originally had a flying cage carried by four winged creatures. Mario would start already in the cage and with an autoscroll script, the cage would move along the level. Although the cage can be found in the code, the graphics for it are incomplete. The cage is likely left over from the 'SNES Test Program'.

Spike Tops originally had six legs when they debuted in Super Mario World.

The two ammunition-based enemies in Super Mario World are Bullet Bills and Torpedo Teds. This would make their referred-to names 'Bill and Ted', a possible reference to the film "Bill & Ted's Excellent Adventure". Their Japanese names translate as "Killer" and "Torpedo" respectively, meaning this reference would have been made by the Nintendo of America localization team.

The symbol that you find at the top of "Special World" is really the Super Famicom logo in Japan, and the SNES logo in Europe.

A hidden level is found in the game's code, which seems to be a test level. All unused level sections are filled with this test level, so over 200 copies of this level are in the game.

If you wait in the special world for a few seconds the music will change to a remix of the original Super Mario Bros. theme.

The manual reveals that the sunken ghost ship is actually an air ship that was used by the Koopalings in Super Mario Bros. 3.

The seemingly random symbol on the mail box of Yoshi's House is actually the logo for Japan's postal service.