A fighter ability, more often referred to as a passive ability, character mechanic, or character gimmick is an unofficial term used in fighting games, including the Super Smash Bros. series, that describes special mechanics specific to certain characters (and/or their clones). They can grant said fighter a passive ability, a chargeable meter, extra moves in their arsenal, or mechanics that are not directly linked to their moveset.
List of single fighter abilities
Certain moves (such as Monado Arts, Pocket, or Wonderwing) are commonly associated as that character's "gimmick", and in some cases have special icons on a character's HUD, but because they do not grant the user extra moves and are directly linked to that specific move, they do not truly count as fighter abilities.
List of shared fighter abilities
In addition to the above, certain mechanics and abilities are present on multiple non-clone fighters, but are not universal throughout the roster.