World 7 of Super Mario Bros. 2 (and in turn the original Doki-Doki Panic) only has 2 stages instead of the standard 3 used for stages in the rest of the game. This is due to the plotline in the manual of the original Doki-Doki Panic, where the final page of the book the twins were teleported into was torn out. This detail was not given an equivalent in Super Mario Bros. 2's plotline, and even in the original Japanese release was not mentioned in-game, and as such could come off as an oddity to players of the original version too should they not read the manual.

As of 2023, only 4 licensed IP adapted games have been released on Nintendo's retro game digital download services: Teenage Mutant Ninja Turtles for NES on Wii (which was later delisted on January 26, 2012), Transformers: Mystery of Convoy for NES on Wii, Quest for Camelot for Game Boy Color and GoldenEye 007 for N64, the latter two being on Switch.

Additionally, J.J. & Jeff, Punch-Out!! Featuring Mr. Dream, and Super Mario Bros. 2, all reskins of licensed titles, have been available in their license-less formats.

The NES and SNES versions of Super Mario Bros. 2 contain different insta-kill cheat codes, likely used by the game's developers for debug purposes. The code for the NES version involves pausing the game and holding Up/A/B on a second controller, and then unpausing to lose a life. The code for the SNES version is simpler, where you only need to pause the game, hold L and R, and then press Select to lose a life.

There are a pair of glitches that can be triggered with this code in the NES version. If the code is inputted while riding a Rocket, the health bar will effectively turn invisible by displaying all the heart pips as empty, but the player character will emerge unharmed. If the code is inputted during the transition for walking through a door, the player character will continually fall through the floor and lose their lives until a Game Over is reached.

Super Mario Bros. 2 was the first Mario game to achieve the number 1 spot in the Top 30 section of Nintendo Power, securing the victory with 22790 points. The second place (The Legend of Zelda) had 6941 points.

At the start of World 1-1, the player falls from a door in the sky that is normally impossible to enter. If you hack the game so that there is a platform under the door and enter it, the game will respawn the player back to the start of the fall and remove the platform, forcing you to begin the stage. This also occurs in the Game Boy Advance version of the game.

In a prototype version of the game, the Underground theme was originally meant to be an updated version of the Underground theme from Super Mario Bros. with added kick percussion, but this was scrapped in the final release. A similar-sounding Underground theme would end up being used in Super Mario Bros. 3.

In the prototype version, the characters had no sclera in their eyes. Strangely, this does not affect the character select screen and the end of the game.

There is a full 14 second loop of the music that plays when in Subspace (based on the original Super Mario Bros.), which cannot be heard as the game boots you out after 7 seconds automatically. It can be heard easily when entering Subspace with a Star affect, then exiting Subspace just before the invincibility wears off.

It's possible to defeat a Phanto through a combination of both the stopwatch and an invincibility star. However, it will simply reappear when entering a new area.

In the prototype version of the game, the title screen was presented in a sepia tone, rather than the red & blue colors in the final release. The story was also slightly reworded from the prototype that said Mario heard a "faint" voice, rather than in the final release where it simply states that Mario heard a voice.

The title screen music is a remix of the Underwater Theme from Super Mario Bros..

The Super Mario Bros. 2 manual mistakenly used a few sprites from Doki Doki Panic, such as the Phantos' original form, a magic lamp (which eventually became the Magic Potion), and a heart (which became the Mushroom power-up).

The image of Mario on the game's box art is just a crudely traced version of the one that appears on the Japanese and European versions of Super Mario Bros..

Contrary to popular belief, there is evidence suggesting that Super Mario Bros. 2 was the true sequel to Super Mario Bros. Some time after the original game's completion, Nintendo's Kyoto-based R&D division began working on a vertical-scrolling Mario engine. It became clear early on that a vertical-scrolling game couldn't offer the same quality of platforming as the original Super Mario Bros. Shigeru Miyamoto then stepped in and added horizontally scrolling aspects to the game.

The prototype engine was originally designed around carrying, throwing, and piling up items and featured 2-player cooperative play, which even included the ability to throw other players to hard-to-reach places to progress further in the game. A deal with Fuji Television was struck during development to promote their 1987 Japanese festival the Communication Carnival Yume Kōjō '87 (translated to English as "Dream Factory '87"), and the prototype eventually became Yume Kōjō: Doki Doki Panic. Although cooperative play was dropped, the concepts of vertical scrolling and tossing around items to defeat enemies was incorporated into Doki Doki Panic, and in turn Super Mario Bros. 2. All of this supports the thought that Super Mario Bros. 2 was, in fact, the true sequel.

The American version of Super Mario Bros. 2 was released in Japan under the title Super Mario U.S.A. This is also the name of the game when it was released in Korea.

There are a few mistakes in the end credits. Birdo and Ostro had each others name, Hoopster was misspelled Hoopstar and Clawgrip is known as Clawglip. These mistakes were not fixed in the Super Mario All Stars version, but were fixed in Super Mario Advance.

Instead of keeping track of how many times each character contributed, Super Mario Bros. 2's prototype originally had a "monetary reward" for beating the game. The amount of cash awarded depended on how many times the player died and the deaths of each character were tallied. The unused money tiles can still be found in the final version of the game.

Super Mario Bros. 2 was technically not a unique Mario game, but rather an enhanced port of a Japanese game called "Yume Kōjō: Doki Doki Panic", translated to English as "Dream Factory: Heart-Pounding Panic". The "Dream Factory" part of the name refers to an expensive 1987 Japanese expo organized by Fuji Television called the Communication Carnival Yume Kōjō '87 that showcased various upcoming programs. As part of an ongoing license cooperation between Nintendo and Fuji, the festival's four main mascots became the playable characters in the game, while all other characters were created by Nintendo. It was ported and released in North America with Mario, Luigi, Princess Toadstool and Toad replacing the mascots. This was released in place of the Japanese Super Mario Bros. 2 (known in the US as Super Mario Bros.: The Lost Levels) because Nintendo of America considered it to be too difficult and too similar to the first Super Mario Bros. to compete with rapidly advancing games from rival companies.

Despite now being the default color for them, and being featured in the game's instruction manual, there was only a single red Snifit in Super Mario Bros. 2, in World 3-3. Uniquely, it would would fall off of ledges as it moved, and would change its direction to face the player.

There's a curious connection between Super Mario Bros. 2 and The Legend of Zelda: Link's Awakening. Two characters in the games are actually the same; Mamu in Link's Awakening and Wart in Mario 2. It should be noted that Wart's Japanese name in Mario 2 is Mamu. Both games are revealed to be dream worlds at the end, with Mario 2 taking place in Subcon (short for subconscious) and Link's Awakening taking place on an island created by the Wind Fish's dreaming.