Your eyes flicker open, floating in that brief stage of unawareness before they remember what your own home looks like. Sitting yourself up in your bed, you raise a hoof to your numb, hazy head, trying to remember that… horrible nightmare? Wonderful dream? How could it be so hard to differentiate?

Most of it was a blur; bluish-black vapour. A fearsome… no, beautiful… black mare that touched you so deeply. Talking, there was definitely something important being discussed at some point in the dream. Wait! You remember doing way more than talking! Her tongue was involved. You can’t remember what she tasted like, but you loved it, that much is certain.

You can’t help smirking at what you remember next; yes, it was a good dream. Definitely the best, and most lucid, dream you‘ve had in a long time.

Then you see it. On your bedside table, the empty glass bottle, and not a single wisp of fog to be seen.

But if you thought to empty the bottle in the first place, then it must be real, right? And if the events inside your head were real, then that means your actions were too. And if, in your dream, you had really taken part in the act of lust, that means in reality you’d just… uh oh.

Slowly, you peek under your bedcovers.

“Eugh, c’mon! Gross!”

A quick change of bed sheets later, you decide a shower would be the best way to clean yourself up after that small embarrassment. It’s lucky you live all by yourself.

Glancing out of the window just as you turn the shower on, you notice it’s still dark outside. You must have only been asleep for an hour or two at most. And yet you feel so rested, as if night is the new morning to you. Nah, it’s probably just the invigorating hot shower.

No amount of hot water in the world could stop the chills that shoots through you right now. That voice was real. You heard it as clearly as the night sky outside. It was all true.

Panic grips your chest like an icy claw; every second of your dream, your encounter, comes flooding back. The worst part? There’s no way you can stop her from taking you. She’s already there.

The numbness inside your head becomes a dull throb. The throb turns into pain. The pain into agony. Tripping out of the shower, you close your eyes tightly - the less light glare, the better - and try not to scream as the pain slowly grows worse.

Your sides are burning, growing tighter as if they want to rip you apart from the inside. Your skin starts to itch, to ache, every fur on your body twitching from the slow takeover.

Suddenly, pain tears through your skull as if you had been impaled via the forehead. Your cries do nothing to soothe the stings as your sides burst in unison, your body growing heavier by the passing second.

Just as quickly as it began, the rush of torture stops. Nothing but the low hum of tenderness that covers your every inch.

You take a dare and open your eyes. The bathroom seems a whole lot smaller now. Lifting yourself up to face the mirror over your sink, you quickly discover why.

You stare into the mirror. A monster stares back. A huge, black stallion with glowing eyes like blue-hot fire. A mane and tail of that all-too-familiar mist that writhed as though it had a life of its own. A sharp horn, long enough to skewer any normal pony. Large, black wings, thick enough to blot out the sun.

And he was also one handsome devil, you had to admit.

“Do you like what you see?” your reflection asks, in an unsettlingly feminine voice, “A perfect compromise between you and I, my beloved host.”

You run a hoof through your new mane, and appreciate your newer, sharper teeth with a sinister grin.

“I like what you’ve done with me.” you reply, “But you could have given me a warning before putting me through that.”

“Oh, but you just weren’t big enough!” the reflection chuckles, “You just had to grow a little! As for the pain of sprouting your wings and horn so abruptly, well, now you see why I tend to go for alicorns.”

“So, this body’s mine and yours? To share? You’re not gonna take me over completely like you did with… whoever you had last time?”

“I was planning to, believe me. But just this once, I think we can work out a compromise. On one condition, of course.” You throw yourself a sly wink, as odd as that sounds.

“Name it.”

“Remember your dream last night? The good part of it?” it says. The good part was as fresh as ever in your mind, of course, “If, every once in a while, we… recur that event, say, in our dreams together…”

“Um,” you glance your reflection’s new body up and down, “you mean as a separate male and female, right? I wouldn’t be playing with myself here?”

“Pfft, you say that like you’ve never done that before.”

“I- Wh- You- Th- that part of my mind‘s private, hooves off!”

Nightmare Moon, or rather, her-in-you, stifles a giggle. Not a wicked cackle, but something much softer. She may have become part of you, but you get the feeling you've left your mark on her too. “Quickly changing the subject, dear, I will remain my true, womanly self as I do within you. It is the mare you grew enamoured with after all. Have we an agreement or not?”

“You can see into my mind, Nightmare, you already know the answer.”

Your reflection smirks knowingly, pleased with how fast you're learning.

“Perfect. Shall we?”

That very night, ponies from across the town reported sightings of an enigmatic, black figure, almost exactly like the much-feared Nightmare Moon, taking to the skies over Ponyville. The direction it was seen heading in was towards the Everfree Forest, back to the old Castle of the Royal Sisters.

Some ponies say the thing still dwells there, recovering from its pain suffered by the Elements of Harmony, waiting to strike back once the time is ripe, and bring about night-time eternal once and for all. Others believe it was going beyond the Castle, beyond the forest, to begin life anew and find acceptance and peace of mind elsewhere in the vast, wonderful world.

Nopony knows for certain. Nopony but you and her, of course.

(Spoiler; I… have no idea what fetish you‘ve got this time, I really don‘t.) - Crowley