Although the Maximum damage a character can accrue during a single stock is 999% normally, due to a glitch, the lava in both the Super Mario Maker stage and a Stage Builder stage can make the damage cap exceed the 999% amount. In order for a player to achieve this they must play in a certain layout of Super Mario Maker or a built stage that features lava under impenetrable platforms so the character that is trapped by the lava continually gains damage. If the trapped character is at 999% and the damage increases, it actually is exceeding the cap despite the display appearing to cap at 999%. However, this amount of damage can be seen if the opposing player uses an incredibly weak move (i.e. Mario's Fireball) on the trapped character, which would have higher knockback than usual and possibly OHKO, or if the damaged character is grabbed, as the grab duration (something that's determined by the grabbed character's damage) will last longer than it would at 999%. However, using a certain move that will not OHKO the damaged character, like Mario's Cape, will reset the invisible damage and the character's knockback and grab duration will go back to 999%.
Contributed by PirateGoofy
With the Shadow Moses Island stage making a return, Snake's exclusive Codec Call Smash Taunts also return (which are triggered by rapidly pressing the down-taunt button once as Snake on the stage). However, no new codec calls were recorded, meaning it will only work for characters that were previously playable in Super Smash Bros. Brawl. In fact, all but one of the old Brawl codecs were kept intact so they now contain many awkward slights and inaccuracies.

These include Brawl still being directly namedropped by the Colonel and Otacon instead of Ultimate during Jigglypuff and Sonic's codecs respectively, Mei Ling and Snake still discussing Sheik's transformation move that she no longer has as of Super Smash Bros. for Nintendo 3DS and Wii U as well as the two also referring to Lucario as having his old "purple flames" instead of his new "blue" ones, and Pokemon Trainer still being referred to with male pronouns despite having a new female alt in Ultimate among other things.

The only codec that was edited for Ultimate was Link's, where the Clawshot was excluded from the list of weapons Otacon reports to Snake, as Link's redesign based on The Legend of Zelda: Breath of the Wild removed it from his moveset.
Contributed by PirateGoofy
Luigi, Ganondorf, and Daisy are the some of the few characters in-game to have at least one of their alt colors be inaccurate between the character select screen and actual gameplay. Specifically, Luigi's yellow and green alt has a yellow "L" on his hat on the Character Select Screen but in-game it has a blue/turquoise "L"; Ganondorf, in his purple alt, is shown when selected as having gold accents, but in battle those same accents are silver instead; And Daisy has a gold crown with her white "wedding gown" alt when selecting her but when the character is fighting her crown is silver.
Contributed by PirateGoofy
Piranha Plant's side special, Poison Breath, seems to come from the Paper Mario series, specifically from the Putrid Piranhas from Paper Mario: The Thousand-Year Door. Piranha Plant's "bud" even changes color to match a Putrid Piranha's yellow and red color scheme during the attack. This would make Piranha Plant the only Mario series character to have a move derived from the Paper Mario series.
Contributed by PirateGoofy
When Hero tries to use the spell Zoom indoors or under a ceiling in this game the Hero will instead bonk his head on the ceiling and the spell's teleportation will not work. This is in reference to the Dragon Quest games, where trying to do the same thing in the same situation will garner the same exact result.
Contributed by PirateGoofy
The seemingly unique design for the Belmonts' Vampire Killer whip, with a metal chain, a morning star at the end, and the religious-looking crossguard, is actually very closely taken from two different sources: Castlevania: Lords of Shadow and the Pachinko game Castlevania: Erotic Violence.
Contributed by PirateGoofy
In a Famitsu interview Sakurai revealed that he and his team wanted to introduce aerial Smash Attacks in this game in order to diversify the limited aerial combat of Smash Bros. However, they rejected this for various reasons, including the belief that such attacks were "too complicated" to implement and also that, in Sakurai's opinion, the system would also destroy the game and series' signature balance between casual and competitive gameplay.
Contributed by PirateGoofy
Sakurai and his team were already working on the Byleth DLC before Fire Emblem: Three Houses was even released. The game director had to work with an early developer's build of the game, which he said took quite a long time to finish. This early build was in fact so Top Secret Sakurai couldn't even been seen playing it and he was even forbidden from taking it to his house.
Contributed by PirateGoofy
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Ryo Horikawa (voice of Captain Falcon) revealed that when he was asked to record lines for the Min Min reveal trailer, he thought he was going to re-record alot of Captain Falcon’s lines in game. However, because Captain Falcon’s voice lines have been reused since Super Smash Bros. on the Nintendo 64, he was brought in to simply record ramen slurping sounds for the trailer.
Contributed by SOGESNAKE
Xander Mobus who plays the Announcer and Master Hand and Crazy Hand in the English version of Super Smash Bros. Ultimate also reprises his role as Ren Amamiya/Joker from Persona 5 in this Smash game, making him the only English Language voice actor to play the announcer in a Super Smash Bros. game to also voice one of the game's playable fighters.
Contributed by PirateGoofy
When Sora holds a battering Item or certain other items (such as a Mr. Saturn) he assumes the same idle stance that he did whenever he turned into Valor Form, one of the drive forms in Kingdom Hearts II that allows him to dual-wield two Keyblades, which in turn is also the basis for one of his alternate costumes in this game.
Contributed by PirateGoofy
A Famitsu Column with game director Masahiro Sakurai revealed that Sora was able to get into the game because of a chance meeting that he had with a Disney executive at an unspecified awards ceremony where they expressed how cool it would be for the Kingdom Hearts protagonist to be a part of the Super Smash Bros. roster. This soon lead to negotiations between Nintendo, Square Enix, and Disney that eventually got the extremely highly requested character in Super Smash Bros. Ultimate. Before then, Sakurai admitted he and Nintendo thought getting the Disney-owned character was a total impossibility.
Contributed by PirateGoofy
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When Kirby absorbs Sora and then uses his Magic, it is immediately clear that Kirby does not get a Keyblade of his own. Instead, Kirby uses an ethereal glowing weapon that resembles a keyblade but is entirely made out of light and sparkles that changes color depending on the spell. While this can be interpreted as being a restriction by Disney over the Keyblade's imagery, Masahiro Sakurai on Twitter chalked it up to being done for lore reasons as he said "...only Keyblade Wielders can use Keyblades..." implying that Kirby isn't "chosen" as barer of one and thus has to use the three spells differently.
Contributed by PirateGoofy
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When the Hollow Bastion stage turns into the Dive to the Heart segment, the different Stations of Awakening in the background that reference key Kingdom Hearts characters appear to be censored of any reference to Disney characters such as Mickey Mouse, Donald Duck, and Goofy. However, these censored Stations are actually close replicas of the designs used on coasters that Square Enix produced in celebration of Kingdom Hearts' 15th anniversary, which also omitted the Disney characters.
Contributed by PirateGoofy
Minecraft World's soundtrack was taken directly from two other spin-offs within its series, Minecraft Earth and Minecraft Dungeons. The game's director Masahiro Sakurai stated in a Nintendo Direct that adding in the original music from the game would have been impossible due to the music's ambience not being suitable for the game, also adding that it would "make players relax."
Contributed by Tuli0hWut
When Kazuya is in Rage Mode and the player is using a Pro Controller or a pair of Joy-Cons, the HD Rumble feature in those controllers will cause them to vibrate in a way that mimics the "thumping" of a heartbeat. This can also be felt with a GameCube controller connected to an adapter, although instead of "thumping", it creates a short, light vibration every couple of seconds due to GameCube controllers lacking the HD Rumble.
Contributed by PirateGoofy
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One of the two villains in World of Light, Galeem, may be based on the Seraphim, one of the rank angels in Judeo-Christian religions. Both Galeem and Seraphim have four pairs of wings and a halo, and both devour darkness with light, turning everyone (excluding the game's fighters) into spirits.
Contributed by GamerBen144
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.
Contributed by PirateGoofy
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.
Contributed by PirateGoofy
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.
Contributed by PirateGoofy
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.
Contributed by PirateGoofy
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.
Contributed by PirateGoofy
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During the beginning part of Sephiroth's Supernova Final Smash where everyone turns to the Z-Axis to view Safer Sephiroth, the normally "flat" Mr. Game & Watch can be seen as a 3D model if he is caught in the attack.
Contributed by PirateGoofy
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.
Contributed by PirateGoofy
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. 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".
Contributed by GamerBen144
When Piranha Plant was revealed as the first DLC character, many fans were bewildered, as a generic enemy has never been a playable character in the Super Smash Bros. series before. Despite this, in an interview with Game Informer, Masahiro Sakurai has stated that he never intended to surprise people with the Piranha Plant, and that it was a character everybody would know of.

"The surprise element quickly fades once the announcement has been made. Rather, I believe it’s important to have a good balance as a game. In the past titles in the series, Mr. Game & Watch, R.O.B. and Duck Hunt Dog were some of the examples we offered outside of people’s typical expectations. However, if we don’t have these types of fighters, and we only had typical “hero/heroine” type fighters in the lineup, there’s not much difference. It’s probably not very interesting. Correct? Also, unlike some main characters from some (not widely known) franchises, Piranha Plant is a character everyone knows well."
Contributed by GamerBen144
The plot of the Adventure Mode: World of Light, in which Kirby is the sole survivor of a cataclysmic invasion and must rescue the other fighters, was actually series director Masahiro Sakurai's original vision for the plot of Super Smash Bros. Brawl's Adventure Mode: The Subspace Emissary.

This early storyline was mentioned during a 2008 Iwata Asks interview:
"I had envisioned a more serious tone for the story. Something with some misfortune like a single character escaping total annihilation of his squadron and then fighting back while rounding up his allies."

It should be noted however that Spoiler:this early storyline would be implemented somewhat closer to the end of The Subspace Emissary anyway when Tabuu decimates every fighter turning them back into trophies, while Kirby, Luigi and Ness are revived in separate locations thanks to the three Dedede Brooches.
Contributed by Boyobmas
Jun Senoue, famous for being a lead music composer for Sonic Adventure 1 and 2, said he was insipired to write and arrange Super Smash Bros. Ultimate's "Mega Man 4 Medley" in the style of a Sonic Series composition after he came across a Sonic and Mega Man crossover comic that sparked his imagination. He chose to center his arrangement on the 4th Mega Man game because of fond memories that he had of playing the game at university.
Contributed by PirateGoofy
Abby Trott, the vocalist of the English version of Lifelight, stated in a interview that she actually cried upon hearing that she would be involved in "Super Smash Bros. Ultimate." Trott, herself, was a Nintendo fan and hearing about this made her feel "very special."

“I was lucky enough to have the opportunity to audition through Cup of Tea Productions, and at the time I had no idea what the audition was for. For the first round, I submitted my singing demo. The second round involved singing a requested song (not ‘Lifelight’). I ended up being cast, and CRIED when I found out what the project was. As a life-long fan of Nintendo, being a part of Smash Bros. Ultimate is really special to me. I love ‘Lifelight’ so much.”
Contributed by GamerBen144
Many of the unique titles for each fighter in Classic Mode contain Easter eggs and references. A few examples are:
*Mario's title "Let's-a-Go" is a reference to one of his phrases.
*Link's title "A Quest to Save Darkness" references the plot of most Zelda games where he's on a mission to seal Ganon away.
*Dark Samus' title "The Great Poison Given Form" references the essence she was created from in the Metroid Prime series.
*Kirby's title "Gourmet Clash" references the Gourmet Race minigame from Kirby Super Star.
*Pikachu's title "I Choose You!" is based off Ash Ketchum's signature catchphrase from the Pokemon Anime, as well as the name of the Anime's first episode.
*Luigi's title "Luigi's Nightmare" is likely a reference to his cowardly personality.
*Ness' title "Home to Onett" is a reference to the Homesick status featured in Earthbound.
*Jigglypuff's title "All Original, All 64" is a reference to the fact that Jigglypuff is a member of the Perfect Attendance Crew for being in every Super Smash Bros. game since the original for the Nintendo 64, and the opponents it faces are against other members of the Perfect Attendance Crew.
Contributed by CuriousUserX90
According to Masahiro Sakurai, in an interview with Famitsu, the reason why Kirby (being a creation of Sakurai's) was the only one that survived Galeem's attack was because he was the only one who could plausibly escape it using his Warp Star. This also made the character accessible to starters or newcomers to the game, as a result of his speed and attacks.
Contributed by GamerBen144
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Charizard, Incineroar, the Inklings, and Sonic the Hedgehog are the only characters that take continuous damage when in water. This is in reference to their respective series, as Sonic cannot swim, Inklings are instantly killed when they come in contact with water, Incineroar and Charizard are fire-type Pokémon which are weak against Water-based attacks.
Contributed by PirateGoofy
If one hacks the camera in the recreated Great Bay stage from Melee and points it to the far left, it's possible to see geographically accurate landmarks originally seen in the world of Termina from The Legend of Zelda: Majora's Mask that aren't seen during normal gameplay.

This includes a series of ledges leading to an alcove with a Heart Container inside of it, Fisherman's Island, and the large gated entrance to the Pirate's Fortress, complete with a new design featuring two crossed swords.

These do not appear at all in Melee.
Contributed by PirateGoofy
The voice clip used for when Snake plants a C4 is a clip that originally went unused in Super Smash Bros. Brawl.

It was thought to have originally served the same purpose as it does in Ultimate.
Contributed by Boyobmas
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Taking the camera inside of Dungeon Man on the Magicant stage will allow you to see Brickroad, who was the operator of the man-dungeon hybrid in EarthBound.
Contributed by Boyobmas
Files for Dragonite from the Pokémon series suggest it may have been planned to be summoned from the Poké Ball. While it does not appear as an assist character in the final game, it does appear as a background character in the Kalos Pokémon League stage. Two models for the character exist, with one more in line of those summoned by the player, featuring higher resolution textures.
Contributed by GamerBen144
Unlike other boss characters, Spoiler:Giga Bowser is classified as a fighter in the game's files, even having placeholder slots for alternate costumes.

These are likely leftovers from the previous game, Spoiler:where Giga Bowser appeared as a playable transformation.
Contributed by Boyobmas
Ridley's orange palette swap is in reference to the villain's appearance on the box art of Super Metroid.
Contributed by PirateGoofy
Yoshi's new Final Smash, where he summons an army of multi-colored Yoshis, is a reference to his part in the opening of Super Smash Bros. Melee.
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When Pit gets Star KO'd, he'll shout out that he never learned how to read. This is likely a reference to a scene from Kid Icarus: Uprising Spoiler:when Palutena cuts off his power of flight upon defeating Pyrrhon.
Contributed by CuriousUserX90
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Mirroring a similar easter egg on the Temple stage, the Sheikah text on a platform in the Great Plateau Tower stage says "SMASHBROS" twice.
Contributed by PirateGoofy
According to Sakurai's Famitsu column, he chose to build the game off of the previous entry's mechanics instead of building the game from scratch as choosing the later would have caused a large portion of the game's roster to be cut. This would be due to the fact that more time would have had to be put into rebuilding each individual character.
He also remarked this decision allowed for more focus to be put on other aspects of the game.
Contributed by Boyobmas
Super Smash Bros. Ultimate is the first game in the series that requires players to select a stage before selecting a character in multiplayer matches. In previous entries, as is common in other fighting games, it was the opposite. This is an attempt by Masahiro Sakurai to change up the strategy of the game (specifically stage-character match-ups).
Contributed by PirateGoofy
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Solid Snake's series logo was changed from the FOX emblem that was used in Super Smash Bros. Brawl, to the exclamation point seen when being caught in most Metal Gear Solid games.

This is likely because the FOX emblem (which first appeared in Metal Gear Solid 3: Snake Eater) is also commonly associated with series creator Hideo Kojima and his company Kojima Productions, a former subsidiary of Konami. Kojima left Konami in 2015 and the removal of the FOX emblem to represent the series is likely a biproduct of the split.
Contributed by Boyobmas