This is where the Nightmare Family is revealed and where Nightmare Moon creates herself a Sith apprentice in Revenge of the Nightmare Family & Changling Queen
[Meanwhile, out in the Dark Lands of Equestria, in a dark temple there was the Nightmare Family!]
King Sombra: At last, resurrected. After all these years!
Nightmare Moon: Soon, we will take back what should've been ours! And they'll have to face my new project!
King Sombra: What is this project? You've been working on it for 3 weeks!
Nightmare Moon: You will know soon enough, it is almost complete.
[then 30 minutes later, it was complete as Nightmare Moon and King Sombra stood in the lab room]
Nightmare Moon: Yes, the project is now complete. Arise my new apprentice.
[from the table rises a black alicorn with cat-like eyes and blue armor and a cresent moon with a 51 for cutie mark]
Nightmare Hiro: Hello, my master.
Nightmare Moon: Hello yourself, Nightmare Hiro. My new Sith Apprentice.
King Sombra: It's fantastic, Moon. We now have a new leap to our take over. Now if only I could get an apprentice myself.
Nightmare Moon: Do not worry, you will soon get one yourself. One who is different and strong with the Force. And he will be the key to the Jedi's undoing, once and for all. [the screen fades black as we see Nightmare Moon's eyes glow in the black void for a second before they fade away]