Mary Sue Hunter

A character who hunts Mary Sues in other Fanfic stories to get rid of them. Also, the format of story the Hunter appears in. This genre appears in sheltered corners of many fanfic communities and more openly in some places.

The genre did not exist before The Nineties, that being when the oldest Mary Sue Litmus Tests started circulating.

The hunter will use a definition of Mary Sue most often based on Common Mary Sue Traits, or perhaps just select Original Characters who really annoy her. The Original Character (or more rarely, a retrofit a canon character) will kill, maim, injure, arrest, expose, discredit, "purify", or otherwise remove another Original Character and their influence from an established canon. Think Revenge Fic, but for Mary Sue.

Usually, these stories are done in a style similar to Mystery Science Theater 3000, taking excerpts from some other Fanfic writer's work and building around it. The tone will usually be cynical and satirical.

While some works with this sort of character are revered, random examples of this genre are not as accepted as normal MSTs. Writers are expected to ask permission to MST another fanfic. Mary Sue Hunters will at best humiliate, and more likely kill and humiliate, the Mary Sues hunted; it's hard (but possible, given the right badfic author) to get permission for that, and there is expected to be honor amongst fanfic writers. Thus, these stories tend to get banned from most regular fanfic communities.

An alternative that's more respectful than hunting without permission and easier than getting permission is if the author also creates the Sues in their fics. These will usually be Parody Sues by definition, or the Sues from the author's old fanfics; the stories they appear in probably won't exist outside the Hunter fic, if there.

The big problem with writing this sort of character and this sort of fic is He Who Fights Monsters. The kinds of Mary Sues that most need hunting are the ones who warp the reality of their 'verses to resist it. The more Mary Sues your Mary Sue Hunter can successfully take down, and the easier the takedowns, the more likely her name could land on some other Mary Sue Hunter's list. Also, not all authors or Hunters can reliably tell if an Original Character is a Mary Sue, but Hunters are almost always presumed to be able to tell—they don't generally accidentally attack innocent characters. So statistically, they are slightly more likely to be a Mary Sue than an OC without an agenda. Some works in this genre, inc. the Trope Codifier, have recognized this.

Anime

 * In the Yu-Gi-Oh! fanfic Not the Usual Kaiba, Mokuba seems to be turning into one.
 * In Naruto Veangance Revelaitons, an ending that the author's former stepbrother wrote has Edfred and his boyfriend Muskoka restore the cast to normal, enabling them to kill the hated main character, who easily fell into several Mary Sue categories.

Literature

 * Limyaael wrote The Game Of The Gods, a Lord of the Rings fanfic that has Morgoth playing a game with Varda where he creates Mary Sues and places them in Middle-Earth while his opponents use logic and the rules of Tolkienian canon to kill them.
 * Redwall fandom used to have these. It was headed by a weasel named Kelaiah and a pine marten.

Live-Action TV

 * Narutaki in Kamen Rider Decade is an odd canonical one. Hellbent on making sure Decade does not enter any worlds except the world of Negatives. He does things ranging from rallying the entire world of Riders against him or at one point summoning an makamou to stop him
 * Or, just stands around and screams about how everything is Decade's fault!

Multi-Fandom

 * Self-Extraction is a story about a Badass Normal former BattleTech Pilot who joined the Agency to stop the intrusion of the Dream Maker, a person who lets people live out their fantasies in other dimensions which have in some way caused trouble. Sues range from crushing the toughest folks in Street Fighter, attempting to kill Barney the Dinosaur and becoming an all-powerful demon god just because the person wants to create a CrapsackWorld with several worlds completely empty.
 * The webcomic Mary Sue Academy has a group of Mary Sue Hunters as villains (sort of).
 * Lynching ITP is a set of Play-By-Post Games which combine this with Mega Crossover, usually directed at the worlds of Twilight or The Inheritance Cycle, though it has a tendency to turn into an Ultimate Showdown of Ultimate Destiny with the Sues in the background.

Web Original

 * The Protectors of the Plot Continuum could be argued to be the Trope Codifier for Mary Sue Hunters, as whether or not they started it, they definitely popularised the idea. Different from others in that it has its own shared universe, and different from the description in that the PPC, while claiming to have various rules that prevent Missions from being like bullying, does not ask for permission from a Sue's author before going after a Sue.
 * Similarly, the Anti Cliche and Mary Sue Elimination Society, (Thus, the name) also in its own shared universe but in a much smaller shell. The Society goes up against mostly Parody Sues and Stus, except some authors will choose to use their own former Sues. However, some of the Agents are almost a hop, skip, and a jump from being Sues themselves, and they're only protected by the mighty power of Lampshade Hanging (and being mostly crazy).
 * Dr. Clef (the character, not the author) of the SCP Foundation has a reputation for "decommissioning" Reality Warpers... most of which are terrible Mary Sues written by people who don't know any better.