"Wait here. Nightmare Moon will see you when she returns."
What!?
That wasn't possible. Nightmare Moon had been defeated and restored to Princess Luna by Twilight and her friends almost two years ago. Did something happen to Luna to cause her to turn back into Nightmare Moon? Not only that, if Nightmare Moon was ruling over Equestria, who was the Mare in the Moon that Sunset saw? Unless...
"What's going on here?" Sunset demanded. "When did Nightmare Moon become ruler of Equestria? Where's Celesti-"
"Don't you dare speak that name within the palace walls!" The guard snarled at her. "Where have you been the last two years that you do not know the story of Nightmare Moon's triumphant return from her unjust banishment? How she exacted revenge upon her sister by banishing her to the moon just as she had done to her?"
"But that's not right," Sunset argued. "She was defeated by Princess Twilight and the other Elements of Harmony."
"Who?" The guard asked. "Enough of this! You're clearly making this up as you go along. There is no Princess Twilight, there are no Elements of Harmony, and Nightmare Moon rules all of Equestria with an iron hoof! You will remain silent until the princess is ready to see you!"
Sunset bowed her head in defeat. This guard was clearly not going to listen to her. Rather than continue, she lay down in her prison cell, trying to find something to occupy herself for the time being. Sunset noticed a window looking out into the night sky. She gazed out at the full moon directly above her. On closer inspection, Sunset noticed something about the moon she hadn't before. It had an odd pastel pink and green hue to it. These colours together reminded Sunset of her old mentor.
Could what the guard had said about Celestia be true? That Nightmare Moon had banished her to the moon, as Celestia once did to her a thousand years ago? But why? Why did nothing that was going on here line up with what Twilight had told her about Equestria? These royal guards had never even heard of Princess Twilight or the Elements of Harmony.
The guard captain Sunset had spoken with had left. In his place, two other guards walked down the hall towards her cell. Sunset could hear their conversation as they got closer.
"...and the princess just left with her to go into the Everfree Forest." The first guard explained to his partner. "Whoever that pony was, Nightmare Moon seemed convinced she'd show her some kind of time travel magic."
"And you said she was an alicorn?" The other guard said, slightly hushed. "I thought Nightmare Moon was the only one left."
This got Sunset's attention. An alicorn? Could it be...
"So did I. She banished Celestia and Cadance a long time ago. But this one didn't seem like either of them at all. She was shorter, about the same size as a regular pony, and get this... she had a baby dragon with her."
'Twilight!' Sunset thought to herself. So she is okay, but why doesn't anypony know who she is? What's this time travel magic Nightmare Moon wanted to see? Sunset felt like no matter what she was just overloaded with more and more questions.
Sunset was suddenly pulled away from her thoughts by a bright flashing light through her window. She turned to look out and saw the light coming from the nearby forest. This must be the Everfree Forest, like the guard said. Eventually the light fizzled out, but what was it?
Some time later, a guard opened Sunset's cell door.
"The princess will see you now. Come with me to the throne room."
The guard led Sunset down the halls of the palace. On their way she noticed a lot more bat-pony guards. Nightmare Moon must be quite fond of them. A few servant ponies also dotted the castle, attending to tapestries, dusting sculptures, or sweeping the floor.
Eventually, Sunset was escorted into the throne room. It was a huge, dark room. Guards stood on either side of the room, and right at the back was a throne, on which sat Nightmare Moon herself, peering from the shadows at Sunset with a look of both disdain and curiosity.
"What is your name?" The alicorn asked. Sunset Shimmer had never met Equestria's Princess Luna, she had run away years before her return, but knew the Vice Principal of her own world well. Nightmare Moon's voice was similar, though it was colder. Sunset felt a chill as she looked into the mare's eyes.
"S-Sunset Shimmer, Your Highness." Sunset didn't know what else to do but bow. She had heard terrifying tales about Nightmare Moon as a filly. One misstep while speaking with her could end badly.
"And why, Sunset Shimmer," Nightmare Moon went on, icily. "Did my guards find you sneaking around Canterlot a short while ago? That area is restricted."
"I... I don't know, Your Highness." Sunset answered truthfully. "I don't know how I got there. I was supposed to be somewhere else."
"I've heard interesting things about you from Captain Caelum, Sunset Shimmer." The alicorn continued. "You claim that I should not be ruler of Equestria. That, as memory serves you, I was defeated by a 'Princess Twilight'. Is this true?"
Sunset swallowed. She needed to choose her words carefully here. "That is what I had been told, yes."
"Very interesting indeed." Nightmare Moon gave a slight chuckle. "This Princess Twilight. I presume she is an alicorn, if she carries such a title."
"Yes, Your Highness." Sunset responded. She wanted to protect Twilight. She wanted to lie, but Nightmare Moon's eyes felt like they were gazing into her very soul, and she could sniff out even the slightest stretch of the truth.
"Describe her to me. What is her cutie mark?"
Sunset hesitated. Nightmare Moon was trying to find out if Twilight was the alicorn she had just encountered. If she knew the truth, Twilight could be in danger...
"Why don't I help you? Was it... a purple star?" Nightmare Moon asked. It only took Sunset's eyes lighting up in horror for the alicorn to understand. Her stony gaze turned into a scowl. "So that's who she was, and she managed to escape too."
Sunset sighed in relief. Wherever Twilight escaped to, hopefully she was safe.
"How peculiar," Nightmare Moon spoke. "That both you and Princess Twilight arrive here mysteriously, claiming that my rule over Equestria should not be. Twilight said that she had access to time magic, and you said that you arrived here through a portal."
Sunset froze. She had mentioned the portal to the guards earlier, in her confusion. She couldn't let Nightmare Moon find it. Who knows what kind of destruction she could bring through to the human world.
"My only conclusion is that you both came here from another timeline. One where I was defeated upon my return before I could seize power over Equestria." Nightmare Moon explained. Things finally started to make sense to Sunset. An alternate timeline, but how did she end up here just by going through the portal? Why was Twilight also here?
"You will take me to your portal." Nightmare Moon commanded. "I would like to see this alternate timeline for myself, and correct whatever error led to my defeat."
"That's not exactly how the portal works, Your Highness," Sunset explained. "I guess I did come here from some alternate timeline, but the portal doesn't lead to Equestria. It leads to...." She trailed off.
Nightmare Moon raised an eyebrow. "To where?"
"A different world. One with no magic, no ponies...." Sunset said. She hoped that maybe Nightmare Moon would not be interested in the human world if she couldn't use her magic there.
"I see," The alicorn responded. Her tone, however, seemed curious, rather than disappointed. "And what were you doing in this world? Clearly you are Equestrian, so what reason do you have to in such a place?"
Sunset thought back to that fateful night many years ago. How she fled into the portal after being caught using dark magic. How angry she felt at Celestia for not teaching her what she wanted to learn. She had long since gotten over these feelings, but perhaps...
"I ran away." Sunset frowned. "But not because I wanted to. I had nowhere else to go after Celestia banished me."
This caught the alicorn's attention. "You were banished by my sister?" Her icy tone began to thaw. For just a moment, Sunset could've sworn she sensed sympathy from Nightmare Moon.
"I was her student. Her prized pupil. Surely, one day, I could have even succeeded her as ruler of Equestria. But she saw the potential I had to overthrow her. She was afraid of me." Sunset feigned anger. It was true, however, that she once thought like this.
"Then I see my sister is the same in any universe." Nightmare Moon scowled. "Fearful of those who might take her power from her. I know that all too well."
"I like to come back to Equestria every so often." Sunset continued. "To see how things changed. A part of me wanted to see Celestia miserable. Full of sorrow and regret for what she did to me. But she wasn't. Instead, she replaced me. And this new student of hers got everything that I should have gotten."
Sunset saw Nightmare Moon's eyes light up. She hoped she had connected the dots.
"Princess Twilight." The alicorn said. "She serves Celestia?"
"Yes. Maybe Celestia sent Twilight here because she knew this was a universe where she was defeated." Sunset suggested.
"Then if she has escaped, they will most likely send an army to destroy me." Nightmare Moon muttered.
"This is all very interesting, Sunset Shimmer. Thank you for telling me all of this." Nightmare Moon said as she rose from her throne and walked down towards the unicorn. Her tone had changed completely. Instead of a ruthless monster, the princess sounded almost motherly. Like the Vice Principal Luna that Sunset knew in the human world.
"Of course, Your Highness." Sunset bowed. "I wish I could tell you more, how you might be able to travel to my Equestria, but like I said, I'm not quite sure how I ended up here myself."
"That's quite alright." Nightmare Moon said. "However, I believe you have more than earned your freedom. For the time being, at least, this is a world where the pony who inflicted so much trauma on you is no more." She gestured to the nearby window, where the Mare in the Moon gazed down from the sky at both of them. "You may stay in this world, if that is what you wish."
Sunset was silently relieved. At the very least, she wouldn't be trapped in the castle's dungeon and might be able to do her own investigating and find a way home. Stroking Nightmare Moon's paranoia, though risky, was unlikely to cause any harm to the real Equestria. If Twilight had left, surely the secret to whatever spell she used to come here left with her.
Nightmare Moon walked Sunset through the halls of the castle. The unicorn couldn't help but be impressed by the beauty of the place. She had read about the Castle of the Two Sisters during her studies, but Celestia was never keen on taking her to see it. Sunset imagined that the secluded location of the castle in the heart of the Everfree Forest suited Nightmare Moon better than Canterlot ever could.
"Follow the trail through the forest. It will lead you to a small town called Ponyville. From there, I wish you luck, Sunset Shimmer." The alicorn explained as they reached the castle's entrance. A bridge stretched across a deep chasm, leading to a path into the forest. Sunset was well aware of the dangers of the Everfree Forest but dared not protest at Nightmare Moon setting her free.
"Thank you, Your Highness." Sunset bowed. She turned and left the castle, venturing into the dark forest. She wondered to herself if she was truly safer in here than she would be with Nightmare Moon.
"She won't last 10 minutes in that forest." Captain Caelum said as he approached Nightmare Moon, the pair looked out into the forest as Sunset disappeared into the trees.
"She claims to have once been a student of Celestia. If she was lying, then she will meet her demise. If not, then I know what I'm dealing with...." Nightmare Moon stated ominously as she walked back inside the castle.