Jeanne d'Arc Alter (Avenger) in her Third Ascension outfit. It looks similar to Jeanne d'Arc (Ruler)'s Third Ascension, but is colored black and has a different design for the torso. This is also the only Ascension form where Jeanne Alter has long hair.
There is a modified version of this outfit that Jeanne Alter wears as a party dress during the Shinjuku story event. It also shows up during the Meihousou Most Foul event, and in Fate/Grand Carnival. As of this writing, this dress has not been given an official name, so it is grouped under official alternate costume.