Funny things: We nearly got the same idea: Mine was about a faction (The Umbralian supremacy) from another world who jumped into Equestria in order to get a new home to live. However, Celestia said no to them without realizing the whole situation: Their world was crumbling due to excessive use of magic from the Equestrian (Any benefit in a world is a disaster in the other. IE:Using the elements of harmony) and they needed a new world or they would die.



Angered by their refusal, Solar Flare declared war against Equestria, starting by revealing to Luna her true nature as Selenia Night-Mare and with her help, the Umbralian army seized Canterlot in less than a few minutes.



The Umbralian has their own version of the mane 6 called the Dark 6 (or Mean 6)



Twilight Shadow is the leader of the Dark 6: Mess with her and she won't forget it until you die. Unlike Twilight Sparkle, Shadow study Dark Magic especially the Magic of Fear and in order to do so, she dress as the grim reaper at night and wear a mask with shiny blue eyes that make her look like the grim reaper.



She has a pet Cobra named Slither who has the same role as Spike: He can breath fire, wrap itself around its victim and his venom can cause paralysis or death.



Next up



Darkning Dash.



DD is a member of the Shadowbolts. A team with Equestrian origin. It is the only Equestrian based team allowed to roam freely on Umbralian territory since their leader, Nightshade, has a teeth against the Wonderbolts leader: Her own sister Spitfire.



Vanity



Vanity is a vampony and an artist. Just like Rarity, she like clothes but also make skulls covered with jewelry to represent her vanity. She's responsible for multiple suicides since she always say: ''What's the point of living if you die in the end?''



She has a little sister named Sweetie Bat.



Pinkamena Diane Pie



Pinkamena is a psychotic pony who despise more than anything related to Pinkie Pie. If she see a balloon roaming freely in front of her, she would become angry and want to kill the one who inflated that balloon.



Of all the Dark 6, she's the most random, no body is really safe when she's around.



Bloodyshy



Bloodyshy is a serial killer with a mischievous attitude. She's not the one who would make a fair fight. She use her stare as a way to reveal the savage nature of animals. That way, she just need to finish her victim with a single slash of a knife or any kind of weapons that cause cuts.



Rottenjack



Rottenjack is the executor of the group. The one who enjoy killing the traitors and intruders. Her favorite way is through hanging because she enjoy the face of those who'll die.

She has a sister named Apple Gloom with who she tend to be overprotective even making death threats to the other two DCMC if Apple Gloom get hurt or something.



Selenia Night-Mare



Selenia is the queen of the night and ruler of the dream realm...as a nightmare injector. She used to be Princess Luna but changed after she learned her true nature and the fact that the Equestrian knew she wasn't one of them but tried to hide it.



Filled with anger against her half-sister, she helped the Umbralian seizing Canterlot and use her capacities as ruler of the dream realm to turn dreams into twisted and terrible nightmares where she's the subject. For example: Twilight Sparkle has a big fear of snakes, Selenia would turn into a gigantic Cobra (as reference to Jafar snake)