Black character glitch
The black character glitch is a glitch in Super Smash Bros. Melee that allows the player to use an all-black character. Normally the color scheme is exclusive to a single CPU Link enemy in the event match Link's Adventure. It is a method of the Name Entry glitch, discovered by Exchord92.
The mode must be set on Team Battle. The characters chosen must be all the same, and on the same team. After that, the glitch is induced by starting the match using the Name Entry glitch.
A similar glitch exists in Super Smash Bros. Ultimate, with turning all characters, Assist Trophies and items all black while stages and the background being unchanged. It is currently unknown about this glitch being patched. See here for how to perform it.
The all black character glitch works because when two or more of the same character are on the same team, those same characters have to be the same color. To help identify who's who, the game has sub- colors it throws on these characters. P1 has no sub-color, P2 is lighter, and P3 is darker. Normally, there aren't supposed to be 4 people on one team, but in this case there is, so the game loads the next sub-color, which happens to be all black (there are also "all grey" and "all pink" sub-colors, only available through the debug menu, and the pink sub-color requires a code to load).