Costume

Costumes, also known as palette swaps and color changes, are a feature in Super Smash Flash 2 and Yeah Jam Fury that allows characters to swap between different appearances with different sets of colors and outfits.

In Super Smash Flash 2
Every character in Super Smash Flash 2 will have 12 different costumes, including the default design, with the main purpose of distinguishing players that are using the same character or simply customizing the character to the player's preference. This is one of the many features carried over from the  games to Super Smash Flash 2 and, as such, was absent from the original Super Smash Flash.

Most costumes recolor certain elements of a character's appearance, such as their clothes, skin, hair, or weapons, with each one meant to represent a separate color or style. However, certain characters also have costumes where they wear different kinds of clothing or accessories, such as hats and bows, which often keep the trend of separate colors.

Players can choose their costumes from the character selection screen. In Free for All matches, players can select any of the costumes their characters have available, and each one can be used by only one player at a time. In Team Battle, characters can only change color by changing teams (which only supports three colors: red, green and blue). If team members choose the same characters, the second will have a lighter tint applied to their character; a third member will have a darker tint.

In online matches, if two players select the same costume, the host is forced to use the default color while the other player keeps the color they have chosen. If both players pick the default color, the host uses the secondary color of the character.

List of costumes
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Below is a list of each character's costumes in SSF2, including their order, colors, and any source material the costumes are or may be based on. Costumes listed as 1 are the default costumes for their respective characters. Cells colored denote costumes available to, and  teams, respectively.

Changing Waluigi's costume will also change the color appearance of his, a unique trait exclusive for Waluigi.

In Yeah Jam Fury
After clearing the final level of Yeah Jam Fury, China Shop, the player unlocks the ability to switch between two sets of costumes, referred to as threads, in the settings menu. The first set of threads is simply the characters' default clothes, whereas the second set has each character wearing a golden hat, a golden jacket, green earmuffs, a white shirt, and black pants. In Style-themed and Desert-themed levels, their colors are unaffected. Much like in SSF2, these changes are purely cosmetic and do not affect gameplay.

Trivia

 * The current method for creating costumes in SSF2 was discovered by developer Refurin in April 2019 and involves applying different colors to separate sections of characters' sprites, called palettes, and then applying different colors to those palettes for each costume.
 * Unlike other, more traditional methods of including costumes, this method only marginally increases the game's file size.
 * According to Refurin, this method had not been known or used in Flash before.
 * Prior to Beta 1.2, before the current method for creating costumes was known, all costumes in SSF2 were simple tints and hues applied to the default design of the character. Many of these costumes have garnered strong controversy from the community due to their simple nature, causing them to appear unnatural and unappealing, and improved costumes were one of the most frequently requested features to be included.
 * Although costumes would be improved with updates to the game, former developer Alex Knowles released a video to his YouTube channel in 2015 to explain the process of making costumes and how the developers are only able to do so much with the limitations of Flash, as more complex costumes would likely require far more work and data to include.
 * With the release of Beta, most characters' effects were separated from the characters themselves in order to keep their colors consistent across costumes. However, with the updated costumes, this is no longer necessary.
 * In SSF2, costumes were first presented in v0.4a of the demo as basic tints ranging from red, green and blue, solely for the purpose of Team battles. This remained the same until v0.9a, which incorporated more complex color changes, replacing the old tints.
 * It was originally planned for Yeah Jam Fury to include additional unlockable costumes, including one that switches the main characters Yeah, Jam, and Fury to female counterparts Yeanna, Jammi, and Furia, respectively, with each having a unique voice. They were intended to be used in the Steam and Wii U release of the game before it was cancelled in favor of the follow-up, Yeah Jam Fury: U, Me, Everybody!.
 * Although YJF only contains one set of traditional color changes and its follow-up contains none, the physical appearance of the three playable characters automatically changes in certain themes in both games.
 * Unlocking the costumes in YJF unlocks the Unlocked Cool Clothes! trochieval.