It was a few hours later now, and Nightmare Moon was still walking after her teleport in the dark clouds. They disperse after a day anyway, she doesn't need to clean them up. Thank the gods too, that would be a right pain. She giggles to herself, remembering the looks on their faces as she emerged from the smoke.
"Priceless," she says aloud, with another giggle, not really caring if anyone was listening in.
She's been living low ever since Luna was purged of Nightmare's spirit, she's not had a bad time, the fact that she even has a body now is evidence of that. She's lived in the Everfree Forest ever since, she was even able to re-inhabit certain parts of The Castle of The Two Sisters, which is how she was able to forge the armour she wears and the claymore she wields.
A long time ago, back when Luna was mistreated, Nightmare was a spirit going from pony to pony helping them with problems they encountered. But when she started to try and help Luna, that was when things started to get out of hoof very quickly.
Luna's room was dark and dingy with a wooden floor which was almost rotting, walls of stone brick without a single window, the only source of light was a magical blue flame which Luna herself had to put there. This room had only worsened her feelings of hatred and anger towards her sister and all the ponies who look up to her. Luna was currently laid on her bed, which was literally just a frame with a bit of cloth to cover herself with, she was dream walking solving the few nightmares ponies allowed her to enter.
It was at this time when Nightmare first met Luna. Nightmare was just wandering around the dream realm looking for ponies to strike a deal with where they just bumped into each other. Both of them trying to help the same pony, it was at this point where Nightmare realised that Luna was the pony who needed help most, and then they struck up a deal. Nightmare would possess Luna and help her to build a better image of herself, but this is when things began to go wrong. Nightmare could seize control of Luna if she felt Luna was making a decision that would affect her image negatively, she was also a voice for Luna to consult about decisions.
This method worked at the start, but progress was slow. Nightmare felt that fact affect Luna leading to her making more brash and less thought out decisions. Nightmare tried tirelessly to stop it but the problem with possessing somepony is that you are subjected to their feelings and unadulterated emotions all of the time. The amount of anger and distress Luna had inside of her was enough to corrupt any soul Nightmare's included.
It was this corruption which eventually lead to the very well known attempted coup, leading to Luna and Nightmare being stuck on the moon for a few hundred years. But once they both returned to Equestria Nightmares corruption did also, and now with a desire for vengeance. It was now Luna's job to attempt to rein in Nightmare's murderous attempts against the Mane 6's lives.
Once Nightmare had been purged from Luna's body, she woke up a few hours after outside of the castle of the two sisters, with all of her memories but now none of the corruption is present, and she began to feel an unbearable amount of guilt. She knew however that to progress in helping those she wronged, she would need to act and not mourn. She can wonder about the body she now has later, now it's time to raid the castle and get what she can from it.
Now it was the day the castle didn't look nearly as menacing as it had when she and Luna occupied it in the night. It looked almost welcoming, albeit in a state of massive disrepair, even as she walked through the main doors to the castle she could see pieces of the walls covered in moss and some bricks very loosely holding the castle up. Nightmare began by investigating the castle's kitchen, knowing that there wouldn't be any edible food but at least something she could wash and then use to cook for herself.
Upon visiting the kitchen she found the bare minimum needed to cook for herself all she needed now was actual ingredients that she could cook with. Because of this she decided to see if any bits were left in the treasury which she would then be able to support herself off of for a while. On her journey to the other side of the castle she again remarks on how much it is falling apart, she was pretty far into the castle but the holes in the walls still allowed her to see outside, admittedly she probably caused a few of these holes but she doesn't remember causing all of them.
She passed by the armoury on her way, and by a brief glance through the door she saw quite a few sets of night guard armour left on their stands, not moved since the castle was abandoned. She begins to think to herself about melting all of them down into a single larger set of armour for herself, because pretty much everypony knows who she is, putting her in a considerable amount of danger.
This big armour set can come later however as she now stood in front of the vault door. It stood many metres above her, its massive rotating padlock lit up blue in her magic as she began to input the correct code. She was surprised that the code hadn't been changed in all of the thousand years she was gone. The golden glow of the bits in the vault began to light up the corridor behind her. There was a considerable amount of bits just left here, surprising nopony looted this place once it was abandoned, but hey that doesn't matter all that mattered now is how Nightmare is going to use these bits because she still stood out like a sore hoof.
She knew she couldn't go back to Ponyville at risk of running into those six that purged her out of Luna. She'd have to get looking at a recent map to get her bearings and attempt to find a backwater village that she could sneak through and legitimately pay for the food that she would take.