Below her, the sprawling landscape of the sunlit Ancient Equestria was unfurled, the land dropping off into a harsh black abyss in every direction, instead of curving like the land normally should have. Then again, Celestia's Underworld, like every one, was a plain and not a planet, meaning that even it had limits and endings.
She had been flying upwards for hours...perhaps even days had passed in which she had done nothing but ascend, and yet it seemed as though height wise Celestia' Underworld still had no limit. She had traveled to the end of the world and looked out across the black, throwing stones and watching them instantly dissolve into nothingness, not wanting the same to happen to herself and therefore never flying past the straight lines which ended the world so abruptly.
It had taken her several weeks to fly to the end of the world, and considering she had been going out of her way to stealthily avoid every single pony she saw along the way, it had been a long and tedious journey, made worse when she found out it had been completely pointless to begin with. As she feared, it looked as though this Underworld was too peaceful and perfect to offer any possible gate to Tartarus. It was entirely possible that she could be trapped here...forever.
If that ended up being the case, she had already concluded that it would be better to fling herself into the unknown abyss at the end of the universe then endure another second of this sunny hell she had found herself in. But before that became her final solution, there was still one more possibility; perhaps she could return to the river the same way she had come in...
She had already spent far too long finding Celestia, and she knew that every day that passed was a day that Discord had exclusive reign over Equestria in the land above. Nightmare Moon was not willing to let that drag on for any longer than it already had. She already cringed at the thought of seeing what Equestria would behold after being under his control for three years, but now she was willing to bet at least another had passed and she still was no closer to finding a way out.
Nightmare Moon shivered as she continued her ascent, taking quick gasps of the air she was projecting around herself with magic in order to survive. The oxygen at this height was far too thin to possibly fill her lungs now. She couldn't help but long for the days when she wasn't confined to a physical body and therefore not limited by it's restrictions, but even they were an improvement over what life had been like without a physical form.
The light sound of running water caught Nightmare Moon's attention, and she perked her ears up at the sound and listened more intently. Yes, certainly, there it was! The waterfall!
Letting out an uncharacteristic giggle, Nightmare Moon beat her wings with excitement and soon enough what had once been a light, barely audible ambiance was now the tell-tale deafening roar of the immense cascades of water. And then, when it seemed as though the sound couldn't get any louder, it cut off completely and she was thrown into complete silence. Looking down, she saw that the green plot of land was now gone and in it's place what looked like the night sky. And, just like it was below her, the starry sky was also sprawled up above her as she tore upwards in the opposite direction of the rushing waterfall.
She was back! She'd really made it out! Who would have thought it would have been so simple?!
"Now then!" She said triumphantly, touching down in front of the pathetic looking archway leading to Tartarus. Carefully reaching into the saddlepack she had stolen from some pony back in Celestia's Underworld, Nightmare Moon withdrew a battered envelope that was beginning to curl and fold with age, the block letters proclaiming that it was For Luna already beginning to fade. As long as she could get Celestia's letter to Luna, perhaps her journey would not be completely pointless after all...
Hopefully, Luna was still willing to listen to the mare who betrayed her.
Of course, there was always the other possibility.
"Nope. Nuh uh." Nightmare Moon chided herself for even thinking so. Amazingly, what had once been her sole intention for teaming up with Discord and bringing Luna to him was now a taboo and unthinkable thing. It was still possible, indeed, with Luna gone she could certainly rise up and take her place and not a single one of the stupid mortal ponies would even notice that the moon princess was gone. She would look the same, sound the same, because she would be another mare living in Princess Luna's body. It would be perfect, and she would finally be free of the title of 'parasite.' She wouldn't need another ponies consciousness to live in, she could finally have her own!
Shaking her head free of such malicious intentions, Nightmare Moon walked through the Gate to find Luna and go home.
Luna's eternal prison was hardly the place Nightmare Moon had been expecting it to be, and yet not even remotely what she would have put beyond the Moon Princess. In fact, it was so predictable that it left her surprised, for she had been expecting something a little more creative.
Across the desolate, grey surface of the moon she walked, noting the earthly gravity and the fact that there seemed to be air and sound here. How delightfully convenient.
"Luna!" Nightmare Moon called out, taking advantage of the impossible sound, and listening to her voice carry across the expanse of the moon. "It's...it's me."
With a sudden explosion of teleportation magic, Luna appeared in front of Nightmare Moon wearing a joyous and relieved looking grin.
"Nightmare Moon!" She exclaimed, beaming with happiness. "I was wondering if you would ever return!"
"I beg your pardon?!" Nightmare Moon gawked, taken aback by her enthusiasm
"Where have you been?" Luna chuckled. "Although I'm somewhat thankful it's taken you...what, four years? I've had plenty of time to think about what's happened, both to me and Celestia..."
"I was expecting you to be angry at me..." Nightmare Moon said, still overcome with confusion.
"Oh, I was. I was furious. I was disheartened. I hated you and I hated myself for trusting you." Luna's grin vanished and with a deep breath the enthusiasm seeped out of her voice. "But overtime I realized that we were both wrong about this place. And, by extension, what you thought you did to me, the harm you THOUGHT you inflicted, was simply not present at all."
Nightmare Moon raised an eyebrow and took a nervous step back. First Luna's sudden, intimidating enthusiasm at seeing her, and now these ridiculous claims that 'everything was wrong.' Had...had she driven Luna to insanity?
"Yes, yes, it sounds ludicrous!" Luna sensed Nightmare Moon's wariness. "But please, I know more about this place then anywhere else! This is my domain! Nightmare Moon, this isn't the Underworld or Tartarus or the Realm of the Dead or any of those mythological legends! This is the Dreamscape!"
"No!" Nightmare Moon protested instantly. "I've been here for decades, I know every inch of this place! This is my home! You think I wouldn't know my own home?!"
"I'm not saying it isn't." Luna said. "I agree that it's your home. But your home isn't Tartarus. It's my mind. That's where we are right now. This is—"
"It's not a dream!" Nightmare Moon cut in. "You said it yourself! You don't dream!"
"Exactly why I didn't recognize this place at all. I've spent so long in the dreams of other ponies that my own are foreign and new to me. But think of it, it all adds up! My fears, my regrets, ponies I've wronged and places I've been...this is what ponies dream about. Everypony's Underworld isn't different, everypony's dreams are different!"
"Luna, listen to me. I've been down here since before you first set hoof here..."
"Because it's my subconscious. You're right, you have been. Because you're a part of my mind." Luna explained, relishing in the growing desperation infecting Nightmare Moon's speech, as she tried to argue against the truth.
"No! I'm more than a mere byproduct of your insanity!"
"What do you remember before you knew me then?" Luna asked quizzically, still entirely convinced that whatever delusions of individuality Nightmare Moon thought she had were only that: delusions.
"Luna, it's time I be honest with you. Heaven knows you deserve it." Nightmare Moon sighed, sitting down on the cold moon's surface. "What I am is a...I guess the correct designation is parasite. I'm a creature that feeds on the negative emotions and malicious desires of other living things. I need it to survive. It's like...like, if I try to be good then I starve. But I can't die, I don't have that luxury. I hate what I am and I hate what I have to do, but if I don't then the pain is unbearable. I need to be a monster."
Luna's eyes grew wide with understanding and confusion, and she too sat down on the ground next to Nightmare Moon, looking at her with eyes of a concerned friend, and not a blaming foe. Nightmare Moon was grateful for that, even if she knew she didn't deserve it.
"Then...what are you?" Luna asked, feeling slightly upset with herself for belittling her mere moments ago.
"Well...you're right about the memory thing. I don't really know. All I know is that prior to meeting you, I must've dragged Sombra into darkness as well. When he was...defeated by you, I must have saw potential by the way you..." Nightmare Moon shuffled uncomfortably. "...disposed of him. You were more powerful, your mind harbored more darkness, and the potential for malice and control was always stronger with you then it ever had been with Sombra. But, everytime I meld minds with another creature, it's like I...reset, forgetting whatever I was before almost entirely. You must be right about the dreamscape, I can't really recall anything outside of it, but you're wrong about me being a creation of it."
"What about Discord? He said you and him were..."
"Working together, yes. I sensed his presence the moment me and you came down here. That's where I disappeared to when we first arrived. Him and I had an arrangement; he got your lifeforce and I got your earthly body to use as a vessel. That way I didn't have to be a parasite anymore. It was only after it all happened that I realized I didn't want that anymore if it meant leaving you behind."
"Leave me behind in my own mind. We would've switched places...I would have been the voice inside screaming for control, and you would have been the one in control." Everything was slowly making sense to Luna now. "So then, you could have done it. What stopped you?"
"I told you." Nightmare Moon breathed irritably. "I can't believe you're making me spell this out for you, Luna. I felt guilt for betraying somepony who I cared about. The ONLY pony I cared about. That doesn't change the fact that I'm a monster, though."
"You might be a monster..." Luna said, shaking her head. "But you make up for it by being something more then that. When we were on the moon, you called yourself my friend, and I replied by saying that to call you such a thing would be to 'shake hooves with evil itself.' Well..."
Luna extended a hoof towards Nightmare Moon and gave her a sheepish grin. Nightmare Moon stared at the hoof for a long while, before understanding and grasping it in her own and giving it a firm shake.
"I'm proud to call you my friend, Nightmare Moon."
"I'm...touched." Nightmare Moon said, chuckling. "And also insulted. Well played, Lulu."
Over several minutes of silence, both mares simply stared across the surface of the moon and reflected upon the events that had brought them there in the first place. There was something Luna had been wanting to tell Nightmare Moon for four years, and now that she could she felt incredibly intimidated to do so. Before she had a chance, Nightmare Moon spoke instead.
"You still broken up over your sister?"
"I am." Luna confessed. "But I've also had plenty of time to think about things. And I've decided that my behavior has been considerably childish and impulsive. I can't reverse what I've done, I really can't. It hurts so much, but I need to move on."
"No. Not yet," Nightmare Moon said abruptly. "We need to talk about it. Right now. And it isn't going to be pretty, but I need to hear you say it."
"Say what?"
"That Celestia's death wasn't your fault."
"It was, Nightmare Moon. I'm not going to place my blame on you any longer."
"That night, it was my corrupt magic that caused your judgement to become so clouded, and that caused you to make the choice to not lower the moon."
"I allowed it. I felt your magic flowing, I felt it as far back as the fall of the Crystal Empire. I could have driven you out but I didn't because it felt good. It made me feel powerful...no, it made me feel equal. Equal to my older sister. With ease I could have driven you out but I chose not to because I wanted to grow in strength. And my jealousy fueled that strength."
"Luna..."
"No, Nightmare Moon. Regardless of what you need me to say, I will instead say the truth. Celestia's death is my fault."
Nightmare Moon said nothing, but nodded slowly to show she understood...and, that she agreed. It was the truth, after all. And although Luna in her right mind would never have done what she did to Celestia, it was Luna who allowed her own mind to reach that point. Coupled with her jealousy, her guilty self-loathing of her inferiority to Celestia...it was a disaster waiting to happen. And it had happened, and now Equestria was facing the bitter consequences.
"I...I met you sister, Luna." Nightmare Moon said eventually, withdrawing Celestia's letter and passing it over to Luna. "She's a nice mare. I can see why you idolize her."
"You met her?!" Luna sprung to her feet, completely disregarding the letter. Her face shone with joy and excitement, but the moment she was standing, it quickly evaporated into sorrow. "That's impossible. You probably met some projection I dreamed up."
"It was her." Nightmare Moon shook her head. "She knew things you didn't, she wrote you this letter, I KNOW it was her."
"It's impossible."
"Obviously it isn't, because I MET her!" Nightmare Moon was growing increasingly annoyed. "This might be all one big dreamscape, but somehow, I met her. Maybe I crossed into her dream."
Luna said nothing, although internally she knew that the chance of such a phenomenon was a billion to one. She knew all there was to know about dreamwalking and there was no way the dead and living could share a dream. Of course, she had never been dead, so how would she know?
"Listen, Luna. That letter I brought is perhaps the only bit of information that we gained in this whole escapade. Just read it. You don't have to believe it, but read it."
"I will. Before we return home." Luna said, stretching her wings and yawning. It was clear to Nightmare Moon that she was eager to shift the conversation away from Celestia. "I'm still quite confused about a lot of things. I'm eager to see them solved. It's stunning to think...this whole journey really has been for nothing. What a waste."
"I don't know about waste..." Nightmare Moon said. "If anything, at the very least we both learned a little bit about each other. Before I had absolutely no regard for you, but now I realize I was wrong to think so. Perhaps it's meaningless to you, but I don't feel quite as useless and parasitic. And you don't seem as weak and pathetic."
"I suppose you'll have a bit more trouble justifying insulting me now." Luna chuckled. "At least it was one hell of an adventure. Makes me wonder if traveling to Tartarus and saving Celestia is really possible in the first place."
"I think it is. That's the terrifying bit..." Nightmare Moon said in a serious tone. "You could potentially set out to do what you attempted here. You'd be an idiot to do so, but you could."
"I know better now." Luna blushed. "Funny to think that this is all a dream. Who would've thought that all we need to do to escape is simply wake up."
"Why would Discord do this?" Nightmare Moon wondered.
"I imagine it was a last resort." Luna explained, before diving into what was obviously an explanation she had perfected over the course of four years spent with nothing better to do but wait for Nightmare Moon's return. "The Elements were failing, he knew I was planning an assault against him. As he was breaking free of the Elements, he must have managed to use his re-growing magic to induce a comatose dreamstate that he himself had the capability of manipulating, since he's the Spirit of Chaos and all. Simply fill in the gap between dream and reality with a reasonable transition of me actually being successful in stopping him, and I would be none the wiser to his actions. And I wasn't."
"Right. But why would he do all that?"
"Several reasons. First of all, it's quite possible the Elements had at least a little connection to me, thus still keeping him encased in stone. By using my magic from the inside out, he could successfully use it to break free entirely. Secondly, it presented him with the opportunity of having you take my place. From his perspective, an evil figure like yourself would possess a much lesser threat to him than I would. I don't think he thought of you as a being that possessed morality or motives, and certainly not one who would have any motivation to protect her subjects."
"Wouldn't simply killing you solve that problem right away?" Nightmare Moon pointed out. "If you're in a comatose state up there, and he's free from the Elements of Harmony, I can almost guarantee Discord wouldn't even hesitate."
"That is a fair point," Luna agreed. "I don't necessarily know. But...I think the most likely explanation might be the most terrifying."
"And what would that be?"
"He wants me to return. He wants to have the opportunity of fighting and killing me, and would rather risk failing then revert to something as boring as doing away with me while I'm unconscious. It's not out of his character to do something like that, I've seen him do it in the past. He could've won so easily against me and Celestia all those years ago, but instead he insisted on drawing out the fight as if it were some sort of game."
"That's completely despicable," Nightmare Moon muttered, fury flitting across her glowing blue eyes.
"No objections from me," Luna agreed. "We should get moving. Discord's had free reign over Equestria for four years. Now that you're here, I can finally wake myself up and we can end this."
Nightmare Moon thought upon that last sentence and couldn't help but be filled with an almost child-like warmth. After all she had done to Luna, and yet she had still waited patiently for her return instead of simply leaving her behind.
Luna's magic lit up the area around them, and when Nightmare Moon looked up she saw that Luna was standing with her eyes closed with an expression of content concentration.
"Wait!" Nightmare Moon said abruptly. "Celestia's letter! Aren't you going to read it before we go?"
In an instant Luna's magic dissolved as she opened her eyes. Nodding, she floated the letter out of Nightmare Moon's grasp and yawned again. It looked to Nightmare Moon like she simply did not care about the letter, leading her to believe that Luna truly did not believe that she had met Celestia.
But as Luna read, her apathetic expression quickly changed. As she read the letter over and over again, her face remained alight with almost every emotion possible; happiness, sorrow, confusion, surprise, familiarity. Whatever Celestia had written, it looked like it had impacted Luna quite greatly. Eventually, curiosity got the best of her, and Nightmare Moon shuffled behind Luna, who looked back at her companion and nodded, non-verbally agreeing that Nightmare Moon should read this.
"Thank you, for bringing me this, Nightmare." Luna sniffled, finally breaking eye contact with the letter and floating it back to Nightmare Moon for her to read. Luna used her hooves to wipe away a few stray tears, and sniffled several more times. Nightmare Moon hadn't even realized Luna had been crying. "This has...it's changed everything for me, Nightmare. Thank you."
"Not a problem." She assured, and began to read.