Title: Children of the Nightmare

Main characters: Nightmare Moon, Princess Celestia, Mane Six.

Genre: Alternate Universe, Adventure, Romance(NSFW).

Cannon Placement: During Children of the Night.

Premise:
Princess Luna uses the foals and fillies she's abducted(who are mostly orphans or those with abusive parents) to build her own sexual colony dubbed the "Children of the Night". She "blesses" them with her magic, giving them the ability to connect with through their dreams(in this version the only way she can enter a ponies dream is to bless pony with her magic, the pony must be willing however). She then begins training them in the arts of both strength and pleasure in order to create her own Kingdom. Over the years she repeated the process of abducting as her "children" grow older, having them older generation pass down their knowledge to the new "children".

However many years later (After they defeat King Sombra), Celestia catches onto Luna's attempts to start a colony she attempt's to stop and capture her when she makes a move to gather more children, Luna takes matters into her own hooves and faces off against her sister, becoming Nightmare Moon in the process while a few of her "children" escape, sadly most of the older generation is capture while NM herself is banished to the moon.

Despite being banished to the Moon, NM contacts her remaining children through their dreams, allowing her to stay updated with the current happenings on Equestria. Over the years that pass she subtly influences her colony, having them go through the abduction process while keeping tabs on Celestia herself. They then bless the new children the same way NM herself does, allowing her to enter their dreams and personally influence them.

Finally after 1,000 years have passed, NM makes her escape and reunites with her Children of the Night. They quickly make their new base of operations in the old Everfree Castle(Which they had built secret tunnels under long since after Celestia move to Canterlot). NM alerts her children that despite she no longer being able to use the Elements she can still sense the ones she was linked to; Honesty, Loyalty, and Generosity.

As a result she plans to find the new wielders the Elements have chosen and bring them under her control...