The crowd of ponies goes silent as everyone notices the purple energy radiating from Luna's body, whispers rise in the crowd as everypony wonders what is going on. The ponies who survived the trip into the Crystal Empire guessed that it had something to do with what Sombra had said during the last moments of his time as ruler of the Crystal Empire, they were both horrified and curious as to what was going to happen. The four ponies from the future had a huge sense of dread come over them, from the look of this the last big event they had been waiting for was about to begin.
To everypony's surprise a patch of black appeared on Luna's dark blue coat, now like a virus that patch of black began to spread and spread until Luna's blue coat had vanished completely and now she was a complete contrast to Celestia's white. Her eyes changed too, although no one could really see any difference. The just knew something was off about them. Luna's fearful expression had been replaced by a look of pure pleasure, her grin went from ear to ear and she began laughing maniacally.
More dark energy flowed, this time around her rather than radiating off of her. The energy cleared quickly this time and was replaced by a bright blue armour encasing her torso and the top of her head. Her laughter grew louder and everypony's fear grew stronger, there was something obviously sinister going on here and it appeared to have taken their moon princess away from them.
Darkness suddenly covered everypony... but it was still the middle of the day. Cheerilee spoke up "Look up." she said to them and in doing what she said they all saw that the moon had replaced the sun in the sky. Panic spread and shouts rose in the crowd of ponies surrounding the area.
"Silence!" Luna boomed in the royal Canterlot tone, she sounded mightily pissed off. "You ponies can cower in front of me and beg me all you want but you will never see your precious sun again. You've never appreciated the work I've done to make your nights peaceful. Oh no, you sleep through it instead and now you'll be stuck with the night forever!"
"Luna...?" Celestia gasped. This new Luna turned to her and smiled.
"Yes sister it is me, although, I don't think Luna is an appropriate name for me now. How does Nightmare Moon sound to you. I wouldn't want to change my name without the'better' sister's permission."
"Wha...? I never considered myself better than you." Celestia argued "What has happened to my sister?"
Nightmare Moon let out a crazed howl of laughter "I am your sister. The sister whom no one appreciates, the sister whose deserved attention goes to the sun goddess and the sister who will put up with it no longer."
Dark energy engulfed Celestia now too but unlike what had happened to Luna nothing about her changed, the dark energy vanished and as everyone looked they realised that so had Celestia.
Roars arose from the guards they had brought with them "What have you done to the princess?"
Nightmare Moon let out another laugh "Don't worry she's still alive. How could I kill her when I haven't even destroyed her precious Equestria yet? She's somewhere she can see nature crumble around her and she has a bed. She's going to need some rest over the next few weeks.' she let out a small chuckle "And with three Elements of Harmony around my..." Nightmare Moon looked down at where her necklace should be and gasped. The elements were gone.
She began frantically searching around but found nothing. The guards and the time travellers began smiling, Celestia had taken the Elements of Harmony from literally under Nightmare Moon's nose. The crowd departed, feeling that they'd seen enough. Doctor Hooves stopped his companions "Come on" he said "we've got to get back to camp." It was up to them to find Celestia, the Changelings had left and the guards were scared to go against an Alicorn so they were the only ones who were willing to try..
This had to end soon or everything in the world would die.