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.

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.

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.

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, jokingly stating that it would "make players relax."

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.

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.

Mirroring a similar easter egg on the Temple stage, the Sheikah text on a platform in the Great Plateau Tower stage says "SMASHBROS" twice.

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.

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).

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.

Tekken's Heihachi Mishima was briefly considered for the roster of Super Smash Bros. for Nintendo 3DS and Wii U, but was ultimately replaced with Ryu from Street Fighter. The team thought that implementing Heihachi's movement into the game would have been difficult due to fundamental design differences between the Tekken and Super Smash Bros. series, and instead released a Mii Fighter costume of him. He was once again considered for Super Smash Bros. Ultimate, but his son Kazuya was chosen instead due to him possessing the Devil Gene from his mother Kazumi. This choice was made to implement Kazuya's Devil Powers into midair jumps, smash attacks and special moves, while making the rest of Kazuya's moveset as similar as possible to his normal moveset in the Tekken series.

Sonic the Hedgehog in both Brawl and Ultimate can outrun the F-Zero vehicles on the Big Blue stage from Melee if he has the Bunny Hood equipped. This can also be done in Ultimate with any fighter who is faster than Greninja.

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.

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.

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.

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.

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.

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.

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.

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.