In the game's files are unused animations for when Giga Mac uses the attack for the KO Punch.

In the Taiwan and Hong Kong websites of the Super Smash Bros. for Nintendo 3DS websites, one of the photos is actually taken from the Wii U version. The Wii U version was not released in Taiwan or Hong Kong yet, and was likely just an oversight of the developers.

In Melee, Nintendo 3DS & Wii U, and Ultimate, if the game language is switched to Japanese, Mewtwo will speak in full sentences for some of its victory poses. In English, Mewtwo only laughs during its victory poses and taunt.

Tingle's trophy chronology only mentions his appearance in Majora's Mask. Which is odd considering Tingle's Wind Waker design is used for the trophy, and his role in Wind Waker is mentioned in the trophy's description.

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.

It was considered to make Alph a clone of Olimar with the ability to use Rock Pikmin. However, this idea was scrapped and Alph became a costume swap instead.

According to Masahiro Sakurai in an interview, Pac-Man would have been removed from the roster if Bandai Namco had rejected his redesign of the character with a more classic Pac-Man appearance, as he considered it superior to the designs used in Pac-Man and the Ghostly Adventures.

Super Smash Bros. 4 is the first game in the Super Smash Bros. series where Falco is not unlocked by completing 100-Man mode. This condition was instead given to Wario.

Because the 3DS needed third party support when it was first released, Nintendo appreciated Namco's efforts on Tekken 3D: Prime Edition, and the two companies became closer. This eventually led to Namco Bandai assisting Nintendo in developing Super Smash Bros. for Nintendo 3DS and Wii U.

An alternate version of Kirby saying "Hi!" for his down taunt can be found in the game's files. This version sounds closer to the ones heard in previous games than the one used in the final game.

The promotional artwork for Ryu is a reference to the Street Fighter 2 World Warriors arcade artwork.

On page 292 of the Prima Guide for Super Smash Bros. 3DS / Wii U, it shows a beta image of the roster containing the Mii Brawler icon. Although the individual Mii fighters do not have their own icons in the final game, the unused icons for the Brawler as well as the Mii Swordfighter and Mii Gunner can still be found in the game's data.

The Epona trophy is taken from the 3DS release of Ocarina of Time, rather than the original Nintendo 64 release.

According to Masahiro Sakurai, in an interview with Famitsu, the reason for the addition of the fighter Duck Hunt was for two reasons. The first reason was that he had an interest on adding them for a long time, but was also because of the uniqueness of the character. The second reason was because of the high sales of the game, and he deemed that the game was the high-selling shooting game in the USA.

Corrin from Fire Emblem Fates nearly didn't make it into the game because Super Smash Bros. creator Masahiro Sakurai thought that they had already included too many Fire Emblem characters.
However, Sakurai's team thought that Corrin would be a unique fighter and convinced him to include the character in the game.

The match end tune from Street Fighter II can be found in the game's files. However, a remix of this tune was used instead for Ryu's win theme. The unused tune was most likely a placeholder during development.

If Little Mac accrues 100% of damage during a match, bruises and tape will appear on his face.

The image of Mario and Luigi carrying gifts for Bayonetta is a possible reference to Bayonetta 2, in which Enzo carries Bayonetta's gift boxes in the game's opening cutscene.

The reveal trailer for Roy shows him taunting in front of the Spicy Curry item. This is actually a reference to a Japan-only Super Smash Bros. Melee photo contest. The winner was a photo called "The Ultimate Curry", which depicted Roy taunting in front of the Curry food item.

Inside the 3DS version's files are unused announcer clips for "Boss Battle," "Tourney," "Events," "Coin Battle," "Master/Crazy Orders," "Smash Tour," and "8-Player Smash," suggesting they may have been available for both versions. All of them except for Boss Battle would later be used for the Wii U version.

As for the 8-Player Smash, there is an announcer clip for "Yellow Team." However, because 8-Player Smash was cut for the 3DS version, so did the Yellow Team.

"Special Smash" can be heard in the Sound Test as voice clip 83 for the Announcer in the 3DS version.

There is an unused Announcer clip saying "Smash World," which may have been an early name for Smash Tour. Similarly, the Japanese name for Smash Tour is "World Smash."