Grimdark

Grimdark is a style of writing that, described by Wikipedia, is "dystopian, amoral, or violent". Though Grimdark mostly refers to science fiction works, the term has been used to describe aspects of the My Little Pony: Friendship is Magic universe, and most notably, its fanfiction.

History and usage
"Grimdark" in the context of My Little Pony is mostly used to describe fanfictions and creepypasta, but has been used to describe the show itself. The "Original Bronies" of 4chan described the pilot episode "Friendship is Magic" to be like "Grimdark My Little Pony" with the fantasy setting and build up to Nightmare Moon.

During the weird era of fanfiction from 2010 to 2012, many My Little Pony fanfictions were written and presented as "Grimdarks", stories that either played up the darker aspects of the show or made up newer ones. Many of these stories were labeled as "creepypastas", as they were written around the time the term grew in popularity and were shared around various fanfiction sites, such as Creepypasta Wiki, Fimfiction.net, Pony Fiction Archive and other sites.

Themes and aspects
Grimdark stories played up various aspects of the franchise, such as the existence of attacking and destroying pony settlements, and by extension, 's ultimate fate, what-if scenarios where Nightmare Moon won, stories of "Scootabuse" in which  would abuse and/or murder, stories of cannibalism and/or torture starring  and darkly lewd stories, typically featuring  or the Apple family.

Grimdark artwork
Aside from stories, may artwork was produced in the Grimdark style, typically portraying "demonic" versions of the lovable characters of the show, generally with dark red and black or faded red-tinted coloring, sharp teeth, wicked smiles and various other generally unpleasant things.

Modern usage
Ironically, but perhaps not unexpected, as the show itself got darker, the shock value of these stories dwindled down and while Grimdark fanfictions are still being written, they generally aren't as popular as they once were.

Popular Grimdark
By far the most popular Grimdark story is Fallout: Equestria, a fanfiction so popular it was even referenced in the Fallout games. Other popular Grimdark or Grimdark-like stories include Weather Factory, Cupcakes, Pale Luna and It Takes a Village, the latter of which is actually a generally wholesome story about Spike's love for his friends, but also features Grimdark attributes such as graphic depictions of violence and the aforementioned themes of dragons doing horrific things.

Grimdark-like
Generally, not every story described as Grimdark contained every element of Grimdark stories, likewise, not every story that fit the aforementioned elements really count as Grimdark for one reason or another. These stories generally had softer tones, more somber than brutal or shocking and tended to be about the death of a loved one, rather than the death of a character. Examples of these include the aforementioned It Takes a Village (which didn't actually involve any major character's death, but rather several near-death experiences), In Memory Of, stories featuring Scootaloo and Rainbow Dash, and in general, several stories featuring Spike, as his long-lived nature would evidently cause him to out live his entire Spike's family.