As of March 2021, there are several mistakes, oversights, and omissions made by the "Move List" section of the pause menu. Some of them are as follows:

•Dr. Mario's Super Jump Punch (his Up Special) is described on his page as "hit[ting] repeatedly". however this is false as Dr. Mario's version hits only once at the start of the attack. Oddly, his base character, Mario, Has his version of the attack hit repeatedly but has a different description of the attack on his own page (the Tips menu corrects this).

•The text on Chrom and Roy's pages describing their counters says that both of the attacks send back the opponents attack "at greater force". However, while this is true in most situations, both counters have a cap of 60% damage that they cannot exceed or a minimum of 9.6% that they cannot go under.

•It says Isabelle's fishing rod grab can throw opponents up, down, or forward, with the menu making no mention of her being able to throw her foes backward with the same attack as well.

•King Dedede's Neutral Special description does not state that it can also automatically reflect projectiles, which is a new feature for the character in this game.

•Being a copy-paste of Simon's text, Richter's Holy Water descriptor states that it takes "fire" damage when his version of the attack actually has the "Aura" effect like Lucario's moves.

When designing the DLC character Steve from Minecraft, most of the game's stages were redesigned to accommodate for his Mine neutral special move which allows him to farm certain materials on stage-specific surfaces to then use to craft stronger weapons. However, not every surface has been programmed to mine the materials expected to appear from the surface Steve is standing on. The most notable example of this occurs on most of the trees in the game, where they can produce Dirt materials instead of Wood.

According to Sakurai in a Famitsu column, Sephiroth's inclusion as DLC in this game was his attempt to include more villains and/or bosses into the series as fighters, stating that the inclusion of such characters as playable was "rare". For one reason or another, he felt Final Fantasy VII's lead antagonist was an appropriate choice for this. He also stated that his game developing philosophy for these types of characters was that he wanted them to "feel like bosses" when playing as or against them.

Sakurai and his team originally had different plans for a Xenoblade Chronicles 2 DLC character. He tried to include Rex as a playable character alongside Pyra, at first thinking of an Ice Climbers-like system where the player would control both characters at the same time, but this ended up presenting programming problems including one involving the game's memory capacity due to the size of the characters. He then had an idea of making Rex a background character whenever Pyra fights, in a similar manner to the Pokémon Trainer. He eventually felt this second method would also be taxing to the game and that fans would not be fond of it anyway so it was scrapped. He then came up with the idea to have Pyra be a transforming character (similar to how Zelda and Shiek were before Super Smash Bros. for Nintendo 3DS and Wii U) with her turning into Mythra and additionally have Rex appear only in taunts, Final Smashes, and other extraneous details involving the characters.

By March 2019, with just 13.81 million units sold the that time, Super Smash Bros. Ultimate had usurped Super Smash Bros. Brawl (if one does not count the different versions of Street Fighter II and Super Smash Bros. for Nintendo 3DS and Wii U which Ultimate also surpassed) as the best-selling fighting game of all-time.

According to Masahiro Sakurai, the reason Min Min was chosen as the playable Arms representative out of the game's cast is because Arms producer Kosuke Yabuki personally requested Min Min; Ninjara was among his top choices to appear in the game as well. Yabuki at one point considered asking them to add the entire cast of Arms' lead protagonists as alternate costumes or playstyles instead of just one character.

Although Terry Bogard from Fatal Fury had made it into the game as a downloadable character, Masahiro Sakurai had initially planned to add Mai Shiranui alongside Terry as one of the cameos in the King of Fighters Stadium stage. In the Japanese Nintendo Direct presentation of Terry Bogard, he explained further that he worried that CERO (Japan's video game rating board) would raise the rating from A (for all Ages) to a higher one which was why he reconsidered having her in the game, joking that Super Smash Bros. was only for "good boys and girls".

There are 17 stages in the Super Smash Bros. series that (intentionally) contain the full title of a video game in their English name: Balloon Fight, Duck Hunt, Find Mii, Luigi's Mansion, Mario Bros., Minecraft World, Pac-Land, Paper Mario, Pokémon Stadium, Pokémon Stadium 2, Super Mario Maker, Tomodachi Life, Wii Fit Studio, Wrecking Crew, both stages titled Yoshi's Island, and Yoshi's Story.

Additionally there are Miiverse and the Pictochat stages but their source material’s status as "video games" are debatable.

Tetsuya Nomura, one of the creators of Kingdom Hearts and the series' recurring director and lead writer, admitted in an interview with Game Informer that it was actually him, not Disney, that was almost hesitant for his character Sora to get into Super Smash Bros.:

Steve's win animation after a match was him eating a steak and holding it at waist level, but in a subsequent update after his initial release, the animation was changed to remove the meat after he ate it. Some speculate that this change was made because the way he held the meat after eating made it look like a phallic object.

Ganondorf's design in Super Smash Bros. Melee is based on his appearance in the Spaceworld 2000 tech demo which showcased a fight with Link and himself where he wields a large sword. This large sword only ever appeared in that tech demo and in one of his win animations in Melee. This specific sword would not be used in Ganondorf's moveset until the release of Super Smash Bros. Ultimate in 2018, where his design is based on that same Spaceworld 2000 tech demo as well as elements from his appearance in The Legend of Zelda: Ocarina of Time.

Super Smash Bros. Ultimate's spirit list comes incredibly close to serving as a comprehensive list of all Nintendo IPs as of 2018, but is mostly lacking content from three specific categories:

• Games that did not receive Japanese releases, such as Tin Star, Magnetic Soccer, and StarTropics (it should be noted that characters introduced in localized versions of Japanese releases, such as Rusty Slugger from Rusty's Real Deal Baseball and the Elite Beat Agents, are featured).
• Arcade games that did not receive ports to Nintendo consoles, such as Monkey Magic, Arm Wrestling, and Sky Skipper. The only exception is Sheriff, likely due to his role as an Assist Trophy.
• Games released exclusively through the WiiWare service. Although there is a spirit from the Fluidity series (which originally released as a WiiWare title), the character in question depicted is Eddy, the main protagonist of the Nintendo 3DS sequel, Fluidity: Spin Cycle.

Three of the character origin tips for Super Smash Bros. Ultimate ignore lesser known Nintendo-branded games released by third parties in the 1990s. Two of these tips outright lie: one related to Mario's first utterance of the phrase "Mamma Mia!" (which it falsely attributes to Super Mario 64 and not Mario's Game Gallery) and another claiming that there are only 5 Zelda series games with Link's name in the title (ignoring Link: The Faces of Evil). The third tip on the other hand is worded in an awkward manner, and refers to Luigi's Mansion as "Luigi's first big break as a main protagonist", ignoring the true holder of the title, Mario Is Missing! without technically lying.

It's not known if those first two instances were an honest error, or an intentional attempt to hide the games given that they are generally seen as low quality and are considered to have negatively affected Nintendo's reputation at their time of release.

If a fighter tries to footstool Piranha Plant while the plant is crouching, the footstooler will be met with a biting attack that takes 4% damage. This happens automatically every time even when the Piranha Plant player presses nothing during the footstool. This highly situational attack however can be easily dodged and countered by the attacked player making it useless in high-level play.

One of the few tracks included from Donkey Kong Country: Tropical Freeze within the soundtrack for both Super Smash Bros. for Wii U and Super Smash Bros. Ultimate is "Swinger Flinger". However, actually listening to the track reveals it to instead be the theme for the Bopopolis stage.

This error is not presented in the Japanese versions of these games, where the "Swinger Flinger" track is properly referred to by its Japanese name equivalent to Bopopolis, ふみふみラビリンス (Fumifumi Rabirinsu), or Stomping Labyrinth. In comparison, the actual Swinger Flinger track and stage in the Japanese version of Tropical Freeze is called バインラビリンス (Bain Rabirinsu), or Vine Labyrinth.

Before his career took off as an indie developer, Toby Fox used to play Super Smash Bros. Melee competitively under the old username 'Radiation'.

He is currently the only known competitive Super Smash Bros. player to have a character he has created represented in the series. Alongside the release of Banjo & Kazooie as a fighter, a Mii costume based on Sans from his game Undertale as well as an original remix of the song "Megalovania" were both added to Super Smash Bros. Ultimate on September 4th.

If the New Donk City Hall stage loops three times, or a music track from the game Captain Toad: Treasure Tracker is playing, Captain Toad will cameo on the stage. This references Super Mario Odyssey where Captain Toad will occasionally appear.