CELESTIA: Long ago, when I was still at the University…

RAINBOW: WHAT DOES THIS HAVE TO DO WITH ANYTHING?!

CELESTIA: We’ll get there, don’t worry. To understand what that creature is, you must first understand what happened many years ago.
CELESTIA: Back when I was still at the University…with my sister.
TWILIGHT: [outraged that all her fanfiction is now ruined] Wait…you have a sister?! How did I not know that?!

CELESTIA: Oh, Twilight. You were only a child then…you never had the chance to know her. You would have liked her. And…I think Luna would have liked you too.

The story begins! Celestia and Luna attended University together, graduated together, and took up teaching positions together afterwards. Though they were in separate departments and pursued different passions – Celestia was a roboticist, and Luna an Elementologist – they remained close and often collaborated on projects and research.

(At this point, Twilight suddenly realizes that she has heard of Luna before – or rather, she’s read some of her papers in the University archives. In fact, they’d inspired her particular field of research; many of Luna’s papers had been on the theoretical existence of a sixth Element, and it was her writing that convinced Twilight that it could be a real possibility. But she’d never realized that this mysterious author had been Professor Celestia’s sister!)

Luna was indeed obsessed with the idea of a sixth Element, perhaps even moreso than Twilight was. In addition to writing endless papers on the subject, she took over the lab on the topmost floor of the University, and would spend entire nights up there, trying out one experiment or another. Celestia was never as interested in the subject, but she would sometimes assist her when she had the time, and made sure that Luna didn’t get so caught up in her experimenting that she forgot to do anything else.

CELESTIA: I thought I’d find you up here. You know you missed dinner, right?

LUNA: Did I? Ah, but I knew you would bring me something anyway!

Eventually, however, their relationship began to strain. Luna’s theories weren’t being taken seriously; her papers were tossed right into the University archives with barely a cursory read. She grew jealous of how much attention Celestia’s projects were getting – the awards she was winning for her innovations, all the students she had clamoring for her attention when hardly anyone was signing up for Luna’s classes…and of course Celestia seemed to just take it all for granted.

Celestia, for her part, noticed that something was bothering her sister…but she brushed it off, thinking that Luna just needed to blow off some steam (so to speak) and would get over it. This careless attitude just made Luna angrier, and they began to fight over almost everything, neither of them wanting to back down from the other.

just your average sisterly spat

Luna was being jealous, and Celestia was being insensitive, but they would’ve eventually managed to move past it and make up if things hadn’t then gone horribly, horribly wrong. Because Luna was a brilliant Elementologist, and she was on the verge of a breakthrough…right on the edge of something new, and something powerful.

Elements are very receptive to emotions. It’s very important to brew them in the right state of mind – never with negativity, never with anger, and never with hatred. Never, ever just after having yet another fight with your sister, after months of arguments and bitterness and hurt feelings.

Celestia did eventually come to apologize…

CELESTIA: ‘Now, Luna, I know we’ve had our differences lately–’ No…‘Now, Luna, we both said some things we didn’t mean…’ …that’s just patronizing. I guess I’ll wing it…
CELESTIA: …Luna?
CELESTIA: Luna?!

…but she was too late. Whatever Luna had made, it was worse than any kind of corrupted Element ever on record – and it was getting bigger, eating up everything in its path.

Celestia tried to wade through it and drag her sister to safety, but it was growing too fast and Luna was too far in. Even worse, the Element had burned through her shoes and was making its way up her legs. The only thing it didn’t seem to be able to eat through was metal, so unable to think of anything else, Celestia activated the lab’s crisis system and sealed it off before it spread to the rest of the University.

Then, before the corrosion could spread past her legs, she had to give herself an emergency augmentation. All in all, not a very good day for her.

Afterwards, once she had a chance to study the situation, Celestia realized something: she had no idea how to save her sister. She knew some Elementology, but she was nowhere near Luna’s level, and even if she had been she had no idea what Luna had done to make the Nightmare. The best she could do was kind of freeze it while it was inside the lab (cough magic science cough), so at least Luna wouldn’t get any worse while she tried to figure out how to save her.

Based on what she salvaged from Luna’s notes, Celestia reasoned that, given enough time, the Nightmare would eventually go dormant, or at least become significantly less dangerous. If, in that time, she could find someone brilliant enough to understand what Luna had been doing, someone who could maybe neutralize the effects of the Nightmare…maybe Luna would have a chance.

She began keeping tabs on up-and-coming scientists, though it wasn’t until she was checking back on that poor boy who’d lost an arm that she noticed his younger sister. She was just starting to seriously pursue Elementology, but Celestia could already see that she was incredibly smart, and creative, and…well, she reminded her a lot of how Luna had been.

So Celestia offered to mentor her personally, and over the years she watched as Twilight grew into a talented scientist, with even more potential than Celestia and Luna themselves.

TWILIGHT: Y-you think I’m smart and talented?

CELESTIA: Of course! That’s why I had asked for your help…

Celestia had decided that if anyone could save Luna, it would be Twilight. But just in case, she assigned her to make some friends – friends made out of metal, who wouldn’t be affected by the Nightmare if something went wrong.

So, when the time was right, she called Twilight up to the University to explain things and ask for her help…except she’d underestimated the power of the Nightmare, and how long it would take for the feelings behind it to cool. It hadn’t gone dormant at all – if anything, it had become stronger.

Fortunately, it seems Celestia made the right choice in protégé. Twilight and her friends not only stopped the Nightmare, the combination of their Elements and the feelings of their friendship reversed the corruption completely, turning it into the sixth Element that Luna had come so close to creating.

FLUTTERSHY: …does it count if it was by accident?

RARITY: An accomplishment is an accomplishment, dear.

CELESTIA: …I’m truly sorry that you were hurt, Twilight. Obviously, this isn’t quite how I intended things to go. Perhaps I don’t have the right to ask you this now, but…

Celestia explains that although the Nightmare was neutralized, Luna’s body was so severely damaged that she requires extensive augmentation in order to survive – and the new Element is the only one she’s responded to. Twilight’s experience with both robotics and Elements will be of invaluable help in rebuilding Luna’s body.

TWILIGHT: Are…are you saying that you want MY help in working on this revolutionary augmentation…with you?

CELESTIA: Of course, only if you want–

TWILIGHT: YES.

Twilight and Celestia immediately begin making plans, because why wait until you’re out of the hospital and medically cleared? As for the bots…

RAINBOW: …I still don’t know what’s going on.

LUNA

Some time later…

LUNA: …Cel…e…?

…and that’s the end of the Nightmare arc!

Twilight and her friends have made up, discovered a new Element, gotten Twilight augmented, and rescued Celestia’s long-lost sister. Pretty good, considering they kind of got thrown into all of it with no idea what was going on.

But hey, all’s well that ends well, right?

I melted off 3/4s of your limbs? Ha ha, hilarious!

AFTERWORD

So, the Nightmare arc was intended to (…very roughly) follow the events of the first two episodes: Twilight fails at making friends, gets in over her head, and it takes the combined power of all six of them to defeat Nightmare and rescue Luna. (Meanwhile, Celestia could’ve avoided the whole thing by just telling everyone what was happening.)

I kind of rushed through a lot of it, and it’s largely focused on Celestia and Luna (…they’re my favorite characters…), but I had wanted to also show more of Twilight trying to fight off the Nightmare, as well as each of the bots helping to save her – Rainbow flying them all there, Fluttershy protecting her with her wings, Applejack kickin’ stuff, etc. Oh well, just imagine that it would’ve been really cool.

A lot of people guessed at what Nightmare/Luna was going to be, and a couple of you actually got pretty close! I think it would’ve been much more obvious once we started getting into what the Elements were, and how this had turned into more of an alchemy-based universe than a machine one.

This was the only arc I had fully planned out, so the rest won’t be a story, but just talking about things I wanted to do and had in mind for other characters. I hope you enjoyed what I’ve had to show, and the other ideas I had for this universe!