If the player tries to make Mario slide while wearing a Hammer Suit, Mario will go into the suit's shell. However, if Mario obtains the Hammer Suit while sliding, an animation of Mario sliding while wearing the Hammer Suit is used. This is the only time this animation can ever be seen.

Over 30 new levels were created for the Game Boy Advance release of the game, Super Mario Advance 4: Super Mario Bros 3. In order to access these new levels, the player requires an e-Reader for Game Boy Advance and the various e-Reader Level Cards. To transfer the levels, the player would require 2 Game Boy Advance systems, the e-Reader, a link cable, and a copy of the game. Because of this, these levels have mostly fallen into obscurity.

Only 10 Level Cards were released in North America, while the other 20 Level Cards were released in Japan.

When the game was re-released on the Wii U Virtual Console and Nintendo Switch Online, all 38 e-Reader levels were unlocked by default as the e-Reader was only supported for the Game Boy Advance.

World 4 (Giant Land) is shaped like a Koopa Troopa.

Inside the game's data are two unused Mario sprites that looks almost identical to the final release, but his overalls are colored pink rather than blue.

If a Muncher is hit with Raccoon Mario's tail attack, it will turn into a block. This trick carried over to the All-Stars version, but not the GBA version, Super Mario Advance 4: Super Mario Bros. 3.

Entering stage 5-3 with a Tanooki Suit and dropping into a Kuribo's Shoe while Statue Mario will grant the player total invincibility from enemies through the remainder of the level.

The king will give a different message than normal if Mario beats an airship wearing either the Frog Suit, the Tanooki Suit, or the Hammer Suit. The King will mistakenly believe that Mario has been transformed into a frog if he is wearing the Frog Suit, believe Mario is an actual raccoon if he's wearing the Tanooki Suit, and if Mario is wearing the Hammer Suit, he'll ask to borrow Mario's clothes.

In the SNES and GBA remakes of the game (Super Mario All-Stars and Super Mario Advance 4), the creatures the Mushroom kings were transformed into were changed from regular animals, such as a dog or a spider, to creatures specific to the Mario series that don't otherwise appear within Super Mario Bros. 3.

In the initial Japanese release, getting hit in any form other than small Mario would revert Mario back to his small form. This was changed in the western release so that getting hit as Fire Mario or any of the suit power-ups reverted Mario back to Super Mario. This was carried on in every platformer Mario game released after Super Mario Bros. 3, with the exception of the original SNES release of Super Mario World.

If Boom Boom is defeated with a Starman, the "?" Orb that appears afterwards will spawn upside-down, and in the center of the arena.

The western version was slightly different compared to the Japanese release. The game was a bit easier, some levels and object placements were slightly altered, the speed of the credits was faster, as well as some other minor details.

This game was the first appearance of the common Mario enemy Boos. They were actually based off of game designer Takashi Tezuka's wife, who would normally shy away from people, but had an explosive temper, triggered by the high amount of time Tezuka was spending at work.

As seen in early screenshots, Koopa Troopas and Hammer Bros. were going to host two mini-games. The minigames were a Question Block and a Dice Block game respectively, which also would have marked the first Mario game to have the Koopas standing instead of on all fours. These mini-games and their hosts seem to have been replaced by Toad.

The Nintendo Entertainment System version of the game was released twice in English, and the worlds were renamed in the second version.

Desert Hill was changed to Desert World.
Ocean Side was changed to Water Land.
Big Island was changed to Giant Land.
The Sky was changed to Sky Land.
Iced Land was changed to Ice Land.
Pipe Maze was changed to Pipe Land.
Castle of Koopa was changed to Dark Land.

Grass Land kept its name.

Many changes were made when porting the game to the Game Boy Advance. The changes were made in order to make the game easier, and to accommodate for the system's smaller screen resolution. These changes include adding coins and power-ups, making jumps shorter and easier, and moving platforms so they could fit on the screen.

The power-up "Kuribo's Shoe" is actually the Japanese name for the power-up, but it was left unchanged for the English release. Kuribo is the Japanese name for Goomba.

Before the US release of the game, gameplay footage appeared in the movie "The Wizard." This served as an advertisement for the game and helped ensure its commercial success.

id software sent a PC demo of Super Mario Bros. 3 to Nintendo hoping to gain authorization to make an official port. Nintendo was impressed but declined, deciding to stick to their own platforms. The demo was based on a test they named 'Dangerous Dave in "Copyright Infringement"', which was a playable recreation of World 1-1 with Mario's sprite replaced by John Romero's Dangerous Dave character.

The three islands on World 7 (Pipe Land) are actually shaped like the Overworld Pipe sprites.

The sound of the warp whistle which is based on the recorder from the original Legend of Zelda, can be heard in the title screen theme of The Legend of Zelda: Ocarina of Time.

The Water Land theme was later used as the theme for the Fairy Fountain in the Legend of Zelda series.

For every 80,000 points you score, a matching card game will appear on the board. This is a chance to receive items such as coins and power-ups. There are only a total of Eight (8) different patterns.

Several of the Koopa Kids' names are parodies of various musical celebrities, most of whom were popular at the time of SMB3's production.

- Iggy Koopa is named after American rock singer Iggy Pop.
- Lemmy Koopa takes his name from Lemmy Kilmister, a British heavy metal artist best known from his work in the band Motörhead.
- Ludwig Von Koopa is named after 19th Century composer Ludwig van Beethoven, and shares his wild hairstyle.
- Morton Koopa Jr. is named after American pop and country singer Morton Downey Jr., now perhaps best known for his self-titled talk show. Morton Koopa Jr. also has a white face with a black star over his left eye, the trademark makeup of guitarist Paul Stanley from KISS.
- Roy Koopa is named after Roy Orbison, and both wear horn-rimmed sunglasses.
- Wendy O. Koopa is named after Wendy O. Williams, an American punk singer.

It's unclear who Larry Koopa is supposed to be based on, but he could be based on Larry Mullen Jr, the drummer for the band U2.

The fortress in World 1 was slightly changed from the Japanese version to make things a bit easier. The right wall in the spike hallway was originally farther away, and the door was under a spike.

The island with the castle in World 3 resembles Japan, with the castle being the location of Kyoto, Nintendo's headquarters.

A popular long-standing fan theory about Super Mario Bros. 3 was that it was actually an elaborate stage play.

The commonly cited evidence that supports this theory include:
•The game's title screen starts with the rise of curtains, and the game ends with the fall of curtains, as well as curtain calls for each World and several characters during the end credits
•Some platforms are hanging down from the "sky" by wires implying it's scenery being hung from the ceiling
•Some platforms are bolted to the wall and cast shadows against the "sky" suggesting it's a backdrop
•If Mario/Luigi kneels on white block platforms for six seconds, he will fall behind them and can walk behind the scenery
•Some platforms are sticking out through carved-out slots in the backdrop suggesting they are being controlled by hidden machines behind the set
•Each regular stage ends by exiting stage left and going "backstage" into the dark goal area
•Every injury or death in a stage is Mario/Luigi messing up the scene (the "Mario was never once in any real danger" part in the attached image is not necessarily true as unintended injuries and deaths can happen in theatre)

One overlooked piece of circumstantial evidence that supports this theory concerns the fact that the Kings of each World that are transformed into different creatures by the Koopalings are never actually seen being transformed into creatures, or transforming back into humans after Mario defeats a Koopaling. The way every Koopaling defeat plays out shows Mario falling from the airship holding the King's magic wand, the scene fades to black, and then the lights come back up inside the castle showing the King already transformed back into a human before either the wand or Mario return to the castle. This suggests that the Kings were never transformed in the first place, because they were all actors waiting to get into place for their scenes, and the transformations are the suspension of disbelief. It should be noted that the Game Boy Advance version of the game partially discredits this by adding cutscenes showing each King being turned into creatures by the Koopalings, but they are still are not seen being transformed back into humans.

In a Q&A interview to promote the release of Super Mario Maker in 2015, Shigeru Miyamoto confirmed the theory, that the game was all a performance.

The box art for the game shows images from earlier stages of the game's development. The image of word 1 has different paths when compared to the final version, and the second image doesn't represent anything seen in the game's final build.

It was once planned for Mario to have a power up that turned him into a Centaur. This isn't as outlandish as it seems; the Tanooki suit was also inspired by the legendary Tanuki.

The Koopalings were based on seven of the game's developers. They were all later named after musicians by the American localization team, as no distinct names were given in the Japanese version. It's also speculated the musical names were chosen because their scepters resemble microphones.

If you let a Chain Chomp tug on its chain 49 times, it will actually break free.