Twilight of Equestria is a Grim DarkMy Little Pony: Friendship is Magicplay by post roleplaying forum. It is set in an alternate universe, Refuge, whose residents regard the original Equestria as a myth. Most of the plot (and by connection, most of the characters) are drawn, one way or another, to a village located in the dead center of Refuge, Nexus. Nexus has plenty of weirdness to go around, with a mysteriously long-lived mayor, an odd-eyed sheriff, and members of the Mafia running around. And they're hardly the weirdest folks in Nexus...It can be found here
This site provides examples of:
Ambiguously Evil: Big Picture isn't evil, but, he basically started a zombie apocalypse (see below).
Dark Is Not Evil: PatchyPart is a genuinely innocent, eager to please young foal who has the misfortune of being made of corpses. Demons also can fall under this category, given that one of them is the sheriff of Nexus.
Darker and Edgier: Oh so much. Pony-trafficking, illegal drugs, organized crime, demons, undead, and all kinds of amorality.
Eye Scream: Five Eyes' 'eyebugs' can crawl in and out of eyes- his own, or others. It is harmless, just looks terrifying.
Fantastic Racism: Demons are frequently responded to with mistrust and, at times, outright hostility. Also a character specific example, Five Eyes has something of a chip on his shoulder against magic-users.
Starstruck is also horribly racist towards non-unicorns.
Frost Breeze comes from a northern village populated entirely by unicorn supremacists
Fantasy Kitchen Sink: Along with earth ponies, pegasi, griffins and unicorns, there are vaguely insectoid demons, flesh golems, a pegasus with mechanical wings, and... a head in a jar?
Fight Club: Nexus has a Fight Club, which acts as its crime hub. Formerly lead by a mare by the name of Ghost, Angel Dust and Black Suit now control its activities.
Current plot developments imply that Celestia banished the ancestors of Refuge's population to their present location, and given Refuge is slated for destruction at the summer solstice, she may well not have stopped there.
Glowing Eyes of Doom: Acheron and Aries have both exhibited these. If they glow, expect imminent maiming.
Good Scars, Evil Scars: Sprocket has a surprisingly evil scar given she's a pretty nice pony- it runs jaggedly across the top of her head and looks like someone attempted to scalp her in the past. And on the topic of scars:
Good Wings, Evil Wings: Ross's cybernetic wings lend him a slightly sinister edge, not to mentioned Acheron's above-stated draconic ones. Ironically Teskivel, who has huge black bat wings, is quite amiable and friendly.
Red Right Hand: Half of Ross's face is horribly scarred, and he has an a-bomb cataract in one eye. He's a scientist trying to engineer Alicorns with particularly brutal methods.
Sherlock Scan: Tidy Queue didn't know anything about you; until he met you face to face, that is. With Queue, everypony wears their heart on their sleeve. Also, their political opinions, honesty, relationship habits, line of work, Habits, favorite flavour of cake, and social security number. Well, maybe not the last two. For those, we'll need five minutes' conversation.
Shout Out: A half ghost character had her ghost and living halves separate in a way very similar to Youmu.
Tidy Queue's narration frequently references or alludes to BBC's Sherlock