Controller modification

A controller modification (commonly known as a controller mod) is a cosmetic or functional change to a stock controller.

Cosmetic mods focus on changing the physical appearance of the controller, such as by recoloring the casing or merging two different shells together to form a two-toned controller. Although rarer, other methods of cosmetic changes can also involve placing LEDs into the casing or changing the physical appearance of individual buttons.

Functional mods involve physically altering aspects of the controller, as to improve its function. Common functional mods include changing either the analog sticks, triggers, or the individual buttons. For the analog sticks, common mods focus on replacing worn-down sticks; while most players generally replace analog sticks with those from identical models, combining two different controllers is not an uncommon practice, and those from non-Nintendo controllers, such as controllers, can be featured. In addition, Brawl, Project M, Smash Wii U, and Ultimate players can choose to remove the springs from the L and R due to the games not recognizing light button presses; Melee players also sometimes alter the length of the springs, as to allow for less resistance to press down the triggers. Severing the rumble motor from the controller, thus decreasing controller weight and preventing the need to constantly have to switch rumble off is also a popular choice. On the most extreme end of the spectrum, players will essentially design entirely different controllers from the ground to meet very specific needs, either to make a design optimized for a certain game and playstyle or to overcome restrictions caused by physical disabilities.

While it is entirely feasible for someone to modify a controller themselves at home, doing so is typically not recommended to inexperienced users, especially with more complex modifications, due to the risks of damaging the controller. There is a market of professional modders that will modify on demand a user's controller for a monetary compensation. Certain modders also sell premade modified controllers online.

Cosmetic

 * Swapping part or all of the shell with one of a different color/design
 * Painting the shell
 * Recolored buttons
 * Engravements/embossments
 * Installing interal lights
 * Tactile or "clicky" buttons

Functional

 * Fixed/mitigated manufacturing errors
 * Control stick/C stick notches (best angles for Sweetspots, Fire Fox, wavedashing, Shield dropping, and drifting.)
 * Removed or cut trigger springs
 * Trigger plugs
 * Recessed buttons/perforated pads
 * Replacement of parts with equivalent parts from a different brand/kind of controller
 * Rumble motor removal
 * Snapback reduction
 * Improved button tactility
 * Adapters to use a controller on an otherwise incompatible system.
 * Design overhauls for accessibility purposes.
 * Add-ons for accessibility purposes.

In competitive play
Modified controllers have been a part of the scene since its inception, but they particularly took off following the release of Super Smash Bros. Ultimate, due to growing frustrations of commercially available controllers often having specific design perks and flaws that are not present in other controllers and vice versa. Fans savvy in mechanical engineering and carpentry eventually decided to come together and develop "perfect" controllers that would have all the benefits of the best controllers while eschewing as many drawbacks as possible. The varying interpretations of "perfect" among fans has led to many different controller designs over the years, including models that excel at specific actions as opposed to the jack of all trades store bought controllers, and models designed to overcome motor function restrictions caused by permanent injuries and physical disabilities. Major corporations have also gotten into the business of hyper-specific controllers, using their resources to make high-quality versions of what fans were already making. This has all led to a steady increase in modded representation at tournaments that has opened the door for those otherwise unable or unwilling to play, overall increasing the diversity of Smash players.

Legality
In general, modifications are tournament-legal as long as said modifications do not perform actions that could not feasibly be done by an average human or perform actions that "break the rules" of the game. For example, Fire Fox notches are legal, whereas an autofire function or the same action mapped to multiple buttons would not be. However, there is no unanimously accepted list of legal mods, so legality is on a case-by-case basis depending on the tournament organizer.