First:

My Little Unicorn Series

Tv Tropes page (for those who want to check it out but don't want to expose their eyes to it):

Number of Past Year Google Hits: 5 on the first page

Explanation: So, once upon a time there was this guy who went by Dakari King Mykan. And he watched My Little Pony: Friendship is Magic and decided he hated it. So he decided to write his own alternate universe without all the things he hated, like Equestria (the story instead takes place in Unicornicopia- I'm not joking, that's the name) the canon characters (He focuses on his own OCs, who are all anthro winged unicorns with special attacks), the message of friendship (replaced with a message of believing- what they're supposed to believe in is unclear), and character depth & development of any sort (He thinks it takes away from the action, so all characters shown basically consist of a name and a gimmick). Throw in a complete and total lack of originality and writing skills, and you've pretty much got the idea.

Second:

The Conversion Bureau

Tv Tropes Page:

Number of Past Year Google Hits: All but 4 results on the first two pages

Explanation: This one is a bit iffy, since by now the general idea of the original fic The Conversion Bureau has become its own genre, with highly varying authors and quality (I believe most people would point to Chatoyance's take on TCB as the worst). However, the original fic is quite poorly done and very well-known in the fandom, so here goes:

Equestria has landed on Earth, and humans naturally want to go there, since they're all evil brutes who've been killing each other off via wars, disease, and the other usual suspects. However, to do so you must (presumably permanently) become a pony, via a serum from the eponymous Conversion Bureaus. A serum that causes the drinker to lose that pesky "human nature" of theirs so they can live in harmony with others. Converts must also adapt to Equestrian culture.

Our Hero goes to get ponified at a clinic conveniently staffed by the Mane Six (despite all of them having canon occupations) and instantly befriends them and goes to live with them in Equestria.

Now, the author's intent was that the wish-fulfillment was the central part of the fic, but the misanthropic undertones that he didn't intend (or at least, not quite so blatantly) were latched onto by some of the creepier members of the fandom, who added some extra horror (Equestria is surrounded by a Barrier that is expanding, sometimes because Celestia's deliberately expanding it to force ponification, and there are pro-pony and pro-human terrorist groups), wrote prolifically, and turned what was originally a very poor fic into a MLP-specific genre.

It should be noted that while the original fic is definitely not as bad as some spinoffs (TCB stories exist that take the entire thing up to eleven), that's less 'well, this is good-ish' and more 'I may have fallen off a giant cliff and am now hurtling at terminal velocity towards my doom, but at least I'm not also on fire'.