-Equestria's Moon, 203 years before Nightmare Moon's return-
Nightmare Moon, the near black coated alicorn with a wavy blue mane that was filled with stars, walked across the surface of the moon. HER moon, and growled yet again. For the last eight hundred years, give or take take three years, she had studied how she had assaulted Princess Celestia, her DEAREST sister, and how she could have lost. She had once been known by another name, Princess Luna, but her anger at her ponies ignoring her and favoring her own sister over her had warped her, changing her into who she was now.
For almost eight hundred years she studied how she had attacked her sister, searching for how she could have been defeated so easily, but the answer was always the same. She had forgotten about the Elements of Harmony, the very tools that the two of them had, at another time in their lives, used against the Spirit of Disharmony, Discord. Princess Celestia had used the ancient gemstones against her, blasting her with enough force to rip her out of Equestria and drop her on the moon, imprinting a shadow of her on the moon's face for the ponies to see each and every night.
And every time she reached the same conclusion her anger returned, an anger that made her ignite her magic and blast part of the space dust that past by into pieces. Just like right now; she spotted an asteroid nearing her moon and her anger took over, weaving her magic into a piercing arrow that tore the hunk of rock to pieces.
"Princess Celestia!" Nightmare shouted, staring up at Equestria from where she was standing, knowing that it was futile to shout as sound died seconds after leaving her mouth, "When I escape my moon, and you know I'll do so, I'll come for you and destroy whatever kingdom, treaties, and friendships you have created! I will cast my Eternal Night upon all of Equestria, so everypony can see just how beautiful it is and treat me with the respect that I deserve!"
She continued to stare up at Equestria, trying so hard to find where Princess Celestia was, hoping that she was looking upon her so she could burn her with her anger. Minutes passed before she finally sighed and looked away from the planet she had once called home, sitting on the rough ground of the moon as her mind wandered once more. There wasn't much for her to do these days besides plan on how she can escape her prison, her precious moon, sooner than whenever Princess Celestia had planned for the sentence to be over.
There were hundreds of spells in existence, most of which both she and Princess Celestia knew by heart at this point, but there wasn't one that allowed teleportation across vast distances, such as from the moon back to Equestria. Nightmare had tried such a spell on the moon, trying to go from one side of the moon, like the one with her face on it, to the other side, where there was nothing but darkness most of the time. But just because a spell didn't do what she wanted it to didn't mean that she couldn't force the nature of the magic to change, which is why she had stored most of her excess magic in the moon itself.
She was betting that a vast amount of magic would allow her spell to transport herself back to Equestria, tearing through whatever enchantments the Elements of Harmony had used on her. That was her theory, one she was prepared to test now that she had gotten her daily rant out of the way and had restored her supply of magic over the previous night. A grin replaced the frown she had been wearing; she couldn't wait to see Princess Celestia's face when she realizes that she escaped from the moon.
Nightmare tapped her hoof against the ground and her magic ignited, flowing around the empty space around her before connecting with the magic that she had stored in the moon itself. Once she was sure the two magics were well connected she turned her attention to the transportation spell, visualizing her return to the castle she had been blasted out of. She closed her eyes and allowed her body to begin the journey from the moon to Equestria, but as she approached her home she noticed something that she never would have thought to account for; a barrier that kept her from performing the action she desired.
The barrier bounced her spell backwards, as if it was supposed to return her to the moon, but when the spell flew past the intended area Nightmare knew she was in trouble. Before she could cancel the spell and return to the moon she felt her body twist at odd angles and she eventually allowed the darkness of space to consume her.
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Nightmare moaned as the feeling returned to her body, but the strange angles that all of her limbs were in made her wonder if she had broken her body. There was a constant pounding that she thought was just her head from hitting the ground, but as she slowly regained consciousness she discovered that it wasn't her head, but rather a crowd. Now that she knew that something was staring at her she began to open her eyes, though the sight she found in front of her came as a surprise; she was in an arena of some kind.
Standing in the center of the ring were two creatures, each of them carrying a suit of armor, a weapon attached to their belts, and what she assumed was a shield on their other side. As she stared at them she found that they stood up straight and walked on two legs, though at the end of those legs were some foreign appendages. She continued up their body until she found the second set of legs, but these ones held another foreign appendage that she assumed were for holding the weapons. And their heads were definitely different from a ponies head, though she noticed that the two creatures were staring at her as if they were debating what to do with her.
She looked down at herself and her eyes widened in shock, finding that her body had been twisted into the same shape that the creatures in front of her were, though she was the same dark blue as her original form. She had the same strange appendages on both sets of her legs, but where the two creatures were dressed in different colored armor she was wearing a suit of azure colored armor, splitting to reveal what she assumed was her stomach. She wasn't carrying a weapon or shield, but she knew that she had something she could summon if either creature decided to attack her.
"Good people of the Imperial City." a voice called out, causing Nightmare to look around for whoever was speaking, "Welcome to the Arena. For this match we had two fresh Pit Dogs ready to do battle, but it seems that we've had a last minute entry. Challenger, what is your name?"
Nightmare groaned and tried to pull herself up, but with as foreign as her body was to her at the moment she knew that she wasn't in any shape to fight anything. The fighter wearing the yellow suit of armor, an elf of some kind, pulled out the weapon it carried, a sword she noted, and ran straight at her, seeking to end someone who couldn't fight back. Nightmare's magic ignited and the air around her shimmered, but as the fighter neared her she swung the legs closest to her head and hoped for the best. She heard the clank of metal on metal and looked up, noticing that she was holding a blackened battleaxe and had, somehow, stopped the fighter in her tracks.
Instead of wasting the opportunity that presented itself Nightmare brought herself to a standing position, similar to what the creatures around her were doing, and pushed the fighter backwards. The creature staggered backwards for a moment, but that was all Nightmare needed as she leapt forward and crushed the head of her weapon into the creature's shoulder, cutting through the armor like it was made of butter. The creature's eyes widened in surprise as Nightmare pulled herself back, lifting the battleaxe out before the creature hit the ground, though a few moments later it became clear that it was dead.
The second creature stared at her as she regained her balance, though from what she could see she wasn't sure that this one would leave her alone either.
"Just who are you?" the creature asked, lifting his sword and shield up.
"I am Nightmare Moon," Nightmare replied, a smile appearing on her face as she lifted up her weapon.
The creature charged at her, but instead of letting the attack land Nightmare threw herself to the right and let it move right by her, though she turned around and brought the head of the battleaxe down as hard as she could. The creature rolled out of the way and got back up onto its legs, turning to look at her again before foolishly making another move without studying her. Half a minute later the creature came charging at her again, though Nightmare lifted the handle of her weapon in time to block the attack she knew was coming. The instant she caught the attack she twisted the battleaxe around and drove the head right into the creature's chest, cutting through the armor and its heart with ease.
"Nightmare Moon!" she heard the crowd chant, wondering why they were cheering for her, "Nightmare Moon! Nightmare Moon! Nightmare Moon!"
"Victor from the Blue Team," the announcer exclaimed, cutting through the noise of the crowd, "leave the Arena and and rest! You've earned it!"
Nightmare had no idea why the announcer thought she was on the Blue Team, whatever that was, but rest sounded good and she looked around to figure out where she needed to go. That was when she spotted someone beckoning for her to come his way, so she gathered her weapon and carefully walked across the Arena to where the creature was standing.
"Sorry about that, I had to claim you before the Yellow Team could," the creature said, beckoning for her to follow him, "They were likely going to call the Imperial Guards and arrest you for 'cheating' in an Arena match, since you hadn't picked a side when you entered. I, um, skipped that step and claimed you for my side, but I'm expecting you to do your best and make some money for us before you fall in battle. I'm Owyn, the fight manager for the Blue Team. You come to me for the fights and I send you in, but whether or not you come back alive is up to you.
Do I have your attention yet, Pit Dog?"
"Look, I'll fight as long as I don't end up in prison," Nightmare said, hating how her stay in this strange world was going already, "but I need to know where I am, what all you strange creatures are, and I guess the rules of the Arena. Help me understand where I am and I'll fight with all my power."
Nightmare knew the arrangement was heavily in the creature's favor, but at the moment this was the best option she had that didn't have her end up in jail. She just hoped that she wouldn't regret it in the long run.