As of Super Smash Bros. Ultimate in 2018, only three characters that started out as Assist Trophies became playable in future installments:

•Little Mac, an Assist Trophy in Brawl, then became playable in Super Smash Bros. for 3DS/Wii U
•Dark Samus, an Assist Trophy in Super Smash Bros. for 3DS/Wii U, then became playable in Ultimate
•Isabelle, an Assist Trophy in Super Smash Bros. for 3DS/Wii U, then became playable in Ultimate.

Despite R.O.B. having his grey and white palette in the American version instead of his red and white palette, his Final Smash trophy shows him with his Famicom color palette no matter what version of the game is being played.

According to Masahiro Sakurai, in the November 2014 issue of GameInformer, the reason why both versions were released at different times was done to "keep the debugging schedules separate from each other:"

"The biggest reason was so we could keep the debug schedule separate from each other. Debugging a game this size is a major project involving hundreds of people, and since the two platforms offer pretty different content, we wanted to avoid conflicts during the debug stages. If we were hell-bent on a simultaneous day-and-date release, we would have wrapped up one title, put it on the back burner, and launched both games in 2015. But I doubt most people prefer that."

According to Masahiro Sakurai, in the November 2014 issue of GameInformer, the reason why Super Smash Bros. was released on two different consoles was because he was a “freelance game designer,” and that having a unique version of the game makes it fun.

"The first reason is that I think both portables and home consoles have their own traits that make them fun. I've gone into that in previous interviews, so I'll omit the details here.

One big reason for this approach is because I'm a freelance game designer ... I'm always going to be the center of any Smash Bros. project, but since I don't have my own personal studio, the staff changes in and out with each project. Changing development studios like this also means that you can't build out from the know-how and in-house assets you've accumulated over time.

As a development environment, it's different from a publisher that can work on fighting games, shooters, and open-world titles all at once. For us, even if things look the same, it's all completely different, completely built from scratch. If we started with a console project then moved on to the portable platform, once one team finished up their work, we'd have to wait and hand everything over to another team."

Underneath Link's hat, you can see fully modeled hair that cannot be seen under normal circumstances.

The emulated NES demos featured in the "Masterpiece" collection seem to run NES games at a higher quality than the actual Virtual Console versions they are promoting. This is most evident in how smooth and clear these demos look against the comparatively blurry VC ports.

This is likely due to Nintendo's improved emulation abilities rather than them purposefully trying to mislead fans, as the NES Virtual console was released very early in the Wii U's lifespan and likely used a system similar to that of the Wii.

In the Japanese version, Wonder Pink's trophy had a different pose, and her legs and underwear were shaded to make it appropriate for the CERO rating.

The Wii U version contains unused sounds of Kirby saying "Heavenly Light" and "Explosive Flame", both of which are Palutena's custom Neutral Specials, suggesting that he was originally intended to copy the custom standard specials of other characters.

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 game contains an unused costume selection for Roy, which uses his default color palette without his cape and comes with a number of minor texture differences.

In the June 14th, 2015 Direct, Sakurai stated that the Suzaku Castle stage was the first in the series to have music that changes as the timer gets close to zero. This is false, as the Mushroom Kingdom stage of Super Smash Bros., and the Mushroom Kingdom and Mushroom Kingdom II stages of Super Smash Bros. Melee all have music that changes as the timer gets close to zero. It is however the first stage in the series that changes the music during stock battles when the last opponent standing or the player is down to their final life.

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.

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.

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

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.

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.

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

In the game's files for Mario Circuit is textures for Toads Kart and Toad himself, this suggests that Toads would of raced instead.

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.

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.