In the far reaches of the dream world, there is a place known as the Nightmare Realm, where bad dreams were said to have originally taken form. It was a horrible, sinister place, one that Luna herself had never even visited, for it was said to be forbidden to enter, lest one disturb its sole denizen.
Within the depths of the Nightmare Realm, there lived a creature, or rather, a spirit of sorts, one thought to be as old or even older than time itself. He was nightmare incarnate, feared by all, he went by many names, Icelus, the Boogeyman, but he preferred to be addressed by his favorite name, Phobetor.
There had been a time when Phobetor ruled like a king, presiding over his realm and all that his title entailed. He would send pieces of himself into the dreams of mortals, giving them nightmares and keeping even the bravest of souls up at night with his visions. But eventually, that was no longer enough to satisfy Phobetor. Oh no, to merely frighten mortals in their dreams had become child's play to him, not to mention that he was confined to only roam the dream world. This is what gave way to his desire, to enter the waking world and bring about terror and fear directly to the mortals.
It was a plot that very nearly succeeded, had it not been for the intervention of his counterpart, Morpheus, the spirit of dreams. With his power, Morpheus managed to subdue Phobetor in an enchanted slumber, and then had him bound and chained inside a casket, left to sleep in his realm and unable to terrify mortals. Centuries passed, and like many spirits of old Morpheus eventually faded away, his essence becoming a part of the dream world. As for Phobetor, he remained asleep in his prison, where it seemed that he would not awaken for eternity. That is, until one day...
The dream world had been thrown into chaos, thanks to the work of the Tantabus, a creature of Luna's own creation. While originally created to punish herself for her misdeeds and to keep her from repeating her past mistakes, the Tantabus had fled from her dreams and threatened the dreams of other ponies. Its rampage nearly allowed it to enter the real world, but thankfully, with the help of the Mane 6, Luna was able to stop the Tantabus and accept it as a part of her.
All seemed well, however, the actions of the Tantabus still had an affect on the dream world. When it tried to open a portal, it had sent a disturbance that rippled throughout, all the way to the Nightmare Realm. From within his prison, Phobetor could feel the disturbance, in fact, it stirred him from his sleep. Now that the spell Morpheus had cast had become undone, Phobetor started to become more and more aware of his surroundings. He felt around the confines of his casket, which were small and quite cramped. It made Phobetor want to squirm and writhe with how uncomfortable he felt, but it was too tight for him to even do that.
Giving himself time to get his thoughts in order, Phobetor wanted to claw himself free, to continue with his original plot and enact his anger and wrath upon the mortals, but unfortunately for him he felt considerably drained and still a little drowsy from his slumber. He would need to gather up more power, not just to regain his strength, but also to be able to tear open a portal to the waking world. Phobetor stilled himself and focused his concentration, creating an astral projection of himself.
The projection was not unlike a shadow as it seeped out from the casket, its form was tall, with long thin arms and long spindly fingers. Its eyes glowed crimson and upon its head were two menacing horns, not unlike a ram's. Phobetor could not help but chuckle to himself. While Morpheus had made sure that he wouldn't be able to get out, he hadn't taken into account his astral projections with which, he could bide his time and gather enough power to sustain himself. He ordered the shadow to go out and seek dreams to infiltrate.
Quick as a bat, the shadow flew out of the Nightmare Realm and to a part of the dream world that one might call limbo. It was the point between the rest of the dream world, and the solitary dreams of mortals. All around in bluish green haze there were little orbs that gently floated like snowflakes on a breeze. Inside the orbs, one could make out one's dreams. The shadow eyed the lovely selection it had to choose from, wondering which dream orb to start with first.
However, its selection was interrupted, as it sensed the presence of another. Not wanting to be detected, the shadow shrank his form to the size of a mouse and scampered behind one of the orbs. It watched and saw Princess Luna come into view. Since as the shadow acted as his master's eyes and ears, Phobetor was able to see the royal alicorn as well.
"Well now, this is interesting."He mused to himself. "It seems there's still someone who is able to walk among dreams. Hmm, I'll have to take care that I don't catch her attention."
With that said, Phobetor instructed his shadow to proceed as planned, but to not let itself be known by the Alicorn.
Some time passed afterwards and Phobetor was steadily regaining his strength. His shadow would enter one dream after the next, instill fear and feeding off of it, and moving onto the next meal before or just as Luna arrived to help remedy the situation. Phobetor felt proud of how clever he was being and was reveling in the delicious torment he was creating. It had been so long since he fed on mortals, that he ached for more fear to consume, but he warned himself not to get carried away, lest he cause himself to slip up and allow himself to be put back to sleep.
With the power he'd managed to accumulate, Phobetor felt confident that he had enough power to block out Luna and keep her from interfering with his meals. He decided that he would choose a host to feed off of, using them to help satisfy his appetite until he was ready to break free. But which of his victims should he use? It had to be someone that was a slave to their own worries and fears, someone who would be powerless to stop him and generate a good amount of nightmare energy for him. As his shadow stopped to watch Luna go over her nightly routine, an idea struck him.
Tonight, he would follow Luna through the dreams she enters, to see if there are any potential hosts among them. If not, then he'd go back to selecting one of his previous victims. The shadow did as he was bid, slithering up behind Luna and melting into her own shadow.
As Luna walked among the dream orbs, she was surprised with how quiet tonight had been, considering the string of nightmares she'd had to deal with recently. She'd wondered if the cause had been her Tantabus or perhaps something else, but she didn't know for sure. She broke from her thoughts and caught sight of Fluttershy's dream orb.
"Perhaps I ought to pay her a visit." Luna thought aloud. "With how quiet it's been, it'd be nice to have a quick chat."
Luna entered the orb and into a picturesque setting of a meadow, filled with innumerable blossoms of every color imaginable. Within the meadow, Fluttershy was humming to herself while fixing together a flower garland. Looking up from her work, Fluttershy saw Luna approaching her.
"Princess Luna!" She cried in surprise, jumping up to her hooves. "What are you doing here, is something wrong?"
Luna shook her head. "No, no, nothing is wrong Fluttershy. I merely wanted to pay you a visit. That is, if it's alright."
"Oh, of course." Fluttershy said, giving her a gentle smile.
"Thank you." Luna said, giving a slight bow to her. "So, how have you been?"
"Fine," she answered simply. "I tried going out on Nightmare Night this year, but...it just wasn't for me."
"I can understand that." Luna said, "Not everyone can handle the eeriness the night has to offer."
"That's for sure." Fluttershy chuckled. Her laughter then subsided when she added, "Um, there was something else that had happened."
"Are you referring to the latest incident with Discord?" Luna asked.
Fluttershy's eye's widened. "H-how did you know?"
"Twilight told my sister about it, and she told me."
"Oh."
Luna could easily see that something was weighing on the Pegasus' mind. "Is there something that troubles you, Fluttershy?"
Fluttershy sighed. "I suppose so. You see, during the three day weekend, when Discord got to hang out with my friends, I was happy. I felt like they were all finally getting along and that Discord was starting to get better at being so friendly. But then, when we learned that he'd used the weekend as a means of hurting Twilight's feelings....I just..."
Luna reached out to Fluttershy with her wing, gently patting her on the shoulder. "You felt foolish for falling for his scheme." She said.
Fluttershy shook her head. "It's more than that! All the fun we'd had, the jokes we made, all of them turned out to be a lie. All so that he could teach Twilight a lesson about jealousy and make her feel awful. I thought...I'd hoped that he'd know better. That he was actually trying to make thing better between himself and my friends."
Luna looked at Fluttershy sadly. "I don't know Discord as well as you do, but you need to understand that Discord has existed for millennia. To live as he has to this point, it'll be difficult for him to break his old habits."
"I know." Fluttershy said softly. But what she didn't say to Luna were her doubts over whether she truly knew Discord or not.
From within Luna's shadow the astral projection could smell the fear and doubts emanating from the Pegasus called Fluttershy. Phobetor could also smell it, and it was positively scrumptious! The worries, the insecurities, it made his mouth water and gave him the desire to gobble the little mortal up. He'd made his choice, this little pony would become him feast, and he would gorge himself until there was nothing left of her.
As Luna said her farewells to Fluttershy and prepared to leave, the malicious shadow slipped out from its cover, and with both mares unaware of its presence, wormed its way into Fluttershy's chest, and taking root.