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.

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.

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.

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.

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.

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.

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.

Mewtwo's character art uses the same pose as the one in Super Smash Bros. Melee.

Takamaru was once considered as a possible playable character in Super Smash Bros. for 3DS and Wii U. According to Masahiro Sakurai, due to his low popularity, he was included as an Assist Trophy instead.

The texture for the Skull Kid assist trophy contains an unused portion which seems to be the flute he used in Ocarina of Time and Majora's Mask. It is unknown what it could have been used for, though it's likley he was supposed to use it in some way when the player summons him.

If the player reflects the Starman enemy's projectile, the "SMAAAASH!!" graphic from EarthBound will flash and the starman will be instantly killed.

The game originally had a 4th set of custom moves for all characters. By hacking the game it is possible to activate them, although most of the moves are unfinished, and do not deliver damage.

In Super Smash Bros for 3DS the trophy titled "Luigi (With Poltergust 3000)" is actually wrong. The Poltergust that Luigi is wearing is actually the Poltergust 5000 from Luigi's Mansion: Dark Moon, which can be noted by the green light on the back of it.

This is the first time both Master Hand and Crazy Hand have in-game announcer calls that are used.

Kongo Jungle is the only past stage from the original game to return, with the exception of DLC.

This is the only game in which Kirby doesn't have a new dash attack, but instead reuses the one from Super Smash Bros. Brawl.

According to Masahiro Sakurai, Bowser Jr. was very close to not being included in the game's roster.

In international releases of the game, the Porky Minch trophy's game chronology only mentions his appearance in EarthBound and not Mother 3, even though the trophy description mentions both games and the trophy's design is taken from Mother 3.

Bowser is the only veteran in the game to not have his victory theme ripped straight from Super Smash Bros. Brawl.

When the track "Wrath of the Reset Bomb" is played while on the Reset Bomb Forest, it will actually sync with what is happening on the stage, and as a result, pausing the game will stop the track. This does not happen on the the Omega variant of the stage, nor does it occur at all in Super Smash Bros. Ultimate.