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 Recorder (also known as the Flute or Whistle) In The Legend of Zelda was later used as the sound for the Warp Whistle in Super Mario Bros. 3, and can be heard in the title screen theme of The Legend of Zelda: Ocarina of Time.

The Water Land theme from Super Mario Bros. 3 was later used as the theme for the Fairy Fountains 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 the game's production. The names were chosen by Nintendo of America employee Dayvv Brooks, a longtime music enthusiast who previously worked at music retailer Tower Records and as a radio DJ:

• Iggy Koopa is named after Iggy Pop, an American rock singer and frontman of the proto-punk group The Stooges.
• Lemmy Koopa takes his name from Lemmy Kilmister, a British heavy metal artist best known as the bassist and lead vocalist for the band Motörhead.
• Ludwig Von Koopa is named after 19th century German 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 the American hard rock band KISS.
• Roy Koopa is named after American country singer Roy Orbison, and both wear horn-rimmed sunglasses.
• Wendy O. Koopa is named after Wendy O. Williams, an American punk singer and frontwoman of the shock rock band the Plasmatics.

The namesake of Larry Koopa remains unclear, with multiple explanations emerging over the years. In 2010, the web page for Nintendo's official UK magazine claimed that the character was named after American talk show host Larry King. However, two years later, Brooks himself made an edit on the Super Mario Wiki claiming that the name was actually derived from Larry Mullen Jr., the drummer for Irish pop rock band U2; site staffer Walkazo verified that the account was legitimate. Brooks ultimately denied both claims in a 2015 interview with Kotaku, stating that "There's no real-world equivalent — he's not Larry Mullen Jr. from U2 or Larry King — he just looked like a Larry."

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.