Character customization, officially character creation (キャラ作り, character building), referred to as Custom Move Sets (カスタマイズ必殺ワザ, Customize Special Techniques) in the Smash Direct, is a feature in Super Smash Bros. 4. It allows players to alter several fundamental properties of playable characters and amiibo, particularly their special moves. All non-DLC characters can replace each of their default special moves with one of two variations unlockable through gameplay, with the exception of Palutena and the Mii Fighters, who instead have a selection of completely different specials, which are all unlocked from the start. Certain characters, such as Mega Man, have moves that appear to function significantly differently as well. In Smash 4, the height and weight of Mii Fighters are customizable as well, affecting their speed and other attributes.
In Super Smash Bros. Ultimate, only Mii Fighters can be customized, with custom equipment and custom moves for other characters removed. Mii Fighters can still be customized with special moves and outfits, and additionally can have their voices adjusted as well, but their height and weight are not customizable. Effects similar to those of custom equipment are present in Ultimate's Spirits mode.
Before the Super Smash Bros. Direct where the feature was officially announced, in June 2013, Masahiro Sakurai had stated that players will be able to customize characters in the 3DS game and transfer those customizations to the Wii U game. He had also stated that the customizations would not be alternate costumes, with exception of the Mii Fighters, and that they would not have to be unlocked through repeated tasks.
It is possible to save up to 10 custom versions of each character and 99 Mii Fighters per game file. If custom fighters are allowed via the option button on the character selection screen, then upon selecting a character, all customized versions of that character will show up, and the player can choose which version to play as or against. The same goes for Mii Fighters, with which every Mii Fighter ever created by the player will appear in a list for the player to choose from. Character customization can be enabled when playing locally or when playing online with friends or in certain tournaments, but not when playing online with anyone. Also, some game modes do not allow customizations to be used at all, which includes all the Stadium game modes (Target Blast allowed them prior to version 1.0.8, and still do via Master Orders), All-Star Mode, Trophy Rush (Smash 3DS only), Stage Builder, and certain event matches in Events.
Custom characters and Mii Fighters can also be copied between the 3DS and Wii U versions, and the latter can also be submitted or downloaded online. However, copied customizations cannot be modified at all, requiring the player to have to go back to the customization's game origin to make any changes. Aside from Miis, customizations cannot be shared between identical versions.
The options for customizing movesets appear in the form of "Custom parts", which come in multiple types:
In tournament play
Custom movesets are banned in Smash 4, though a number of tournaments allow their use in side-events. Custom movesets were temporarily legal from March 2015 to July 2015, as part of the Official Custom Moveset Project on SmashBoards, but concerns regarding gameplay balance and logistics issues caused custom movesets to be banned after the conclusion of EVO 2015.