Unused content (SSB4)
Much like Super Smash Bros. Brawl, SSB4 has a reasonable amount of unused character data. The reasons mainly include a combination of time constraints and hardware limitations. This is supported by Masahiro Sakurai stating this during a post-release interview. However, he refused to give any sort of information on what other scrapped characters were, other than stating that characters unlikely to appear in new games in the foreseeable future were given lower priority. It is unknown whether any of the downloadable characters were originally intended for the game's initial release.
Hidden with the games files exist stages that were planned to be included in SSB4, but were not implemented in the final release. For some stages, it remains unknown whether they were meant for the 3DS or Wii U version.
Some of these stages were meant to have hazards or other elements, as the game's files depict file called
There exists unused files in for Wii U for Mushroomy Kingdom and 3D Land; however, the only files remaining in each directory is the item parameter file, meaning these files are mere remnants from for Nintendo 3DS.
When comparing the final game with earlier builds, as well as viewing unused data left on the game disc/cartridge, some differences have been found:
A major amount of content for SSB4, revealed in Famitsu or leaks, were either removed or revamped.
Scrapped mode features
A trophy for the Fire Emblem Awakening character Tharja was initially planned for the game, and the trophy was visible in leaked ESRB footage. Following the release of the game in Japan, however, Tharja's trophy was not found by players on Twitch, and later hacking showed that there was no data for the trophy in the final game, suggesting that it was removed some time after the ESRB footage. The reason for the removal of Tharja's trophy is considered to be related to the game's rating; her outfit as a Dark Mage was likely considered too suggestive and revealing for SSB4's intended E10+ rating, compared to Fire Emblem Awakening's T rating. As the leaked images showed a counter of 686 and there were 685 trophies prior to Mewtwo's release in the final build, Tharja's trophy was the only such trophy removed.
Super Smash Bros. Masterpiece
There is an unused file consisting of text that refers to a Masterpiece of the original Super Smash Bros. for the Nintendo 64, suggesting it was playable at one point. This would've been the only N64 Masterpiece in SSB4 and the first Masterpiece in both Brawl and SSB4 that was actually a game from the Smash Bros. series.
Unused boss icons
Unused boss animations
Interestingly, in the bosses folder, an unused set of strings and attack animations for BossPackun (Petey Piranha's Japanese name) have been found in the code (though the animations are only present in the files of the Wii U version), suggesting he was meant to return as a boss in some capacity.
Several unused gameplay elements can be found within the data of for Nintendo 3DS, some of which ended up becoming integrated into the final build of for Wii U.
Song titles did not seem finalized until late into development. Early in development, the song "Saria's Song / Middle Boss Battle" was named only "Saria's Song" without "Middle Boss Battle" in the title. "Ballad of the Goddess / Ghirahim's Theme" was simply referred to as "Ballad of the Goddess". "Main Theme / Underworld Theme (The Legend of Zelda)" was just referred to as "Main Theme". These can all be seen in this image. The reason is unknown. It can also be noted that the words "Arrangement" in the image were changed to say "Remix" in the final game.