The plan they had developed was for Nightmare to go in first and question Celestia, using the darkness to her advantage to hide her new form, but that plan got blown to pieces when Celestia used her horn to light the room, her eyes widening as she saw what used to be her sister. Celestia quickly used her magic to trap Nightmare against the wall, making her squeal from the pressure being exerted on her body.
Discord and Chrysalis heard the squeal and rushed in, eager to face the rogue Queen and change their timeline. Together they used their magic, one controlling how much chaos was implimented with the spell, the other casting the actual spell, forming a vast majority of stones above the Queens head. It took all of Celestias magic to hold back the torrent of falling debris, making her let Nightmare loose as she fended off the waves of rocks.
She glared at the three figures standing before her, three traitors who wanted to take her place, three...her gaze softened as she noticed the markings engraved into the armor Nightmare was wearing. "Luna...," she said softly, "What are thou doing?"
Nightmare frowned and said, "Sister of mine, I have remembered what thou hast done to get thine kingdom, and I don't approve of it. I have also been told by a shadow, as well as these ponies by my side that thou plans to rise and take the kingdom by storm in a thousand years time."
Celestias face lost all trace of emotion except for anger as she said, "Well then, if it's a fight that you wish, then it's a fight you shall have."
The room flashed with light and Discord and Chrysalis were blinded by the flash. Leaving only Nightmare able to fight Celestia. She scanned the room in search of her sister and saw her sneaking up on the exposed members of the group, posed to strike them down with her magic. Nightmare acted quickly, leaping over her comrades and slamming down on Celestia, making her slide across the floor as Nightmare bombarded her with magic.
She threw invisible punches, grew a tiny ball of iron in Celestias stomach and smashed it around inside her organs, leaving her broken and bruised. Celestia got up and spit out a mouthfull of blood, smiling as she turned to Nightmare.
"Is, that the best you've got," she said.
NIghtmare was driven up into the air, slamming into the ceiling and crushing the air from her lungs. The pressure kept building on her and her bones began to snap in several places, making her scream out in pain.
"Ey, Queen Celestia," a mares voice called out as a large stone was launched at Celestia's horn, "think fast." The rock connected, sending a jolt of magic both ways, crushing Nightmare against the ceiling one more time and resounding with the greatest crack yet, while it simaltaneously launched Celestia back, slamming her into the wall and making a few of her teeth fall out from the impact.
Chrysalis slowed Nightmares desent, laying her softly onto the ground and quickly turned around only to be smashed against the ground. Her jaw connected first, sending a jolt of pain through her entire system. She was lifted back up and slammed into the ground with more force, making several cracks appear along the ground and a few of her broken bones began to pierce the skin.
The process was repeated multiple times, leaving her in tears of agony before the last of the three warriors stood up and said, "You're not going to live any longer than this day Celestia, I can promise you that."
Celestias eyes had a gleam in them as she said, "Don't make a girl a promise you can't keep."
Discord snapped his fingers and the ground beneath Celestia opened up, revealing a chasm below her feet which she mearly laughed at untill Discord snapped his fingers again and her wings as well as her horn vanished.She plummeted into the hole with the screams of somepony who knew her time was up. The Dragonequius snapped his fingers as she vanished, closing the hole behind her as he collapsed from exaustion.
He looked over at Chrysalis to see a smile on her face and he said, "We did it, she's gone. Dead. She's never going to destroy the kingdom."
Suddenly the floor erupted, spewing chunks of the ground in all directions, slamming into the three exausted and broken figures with an amazing force, cutting and wounding them.
The white Alicorn rose from the middle of the hole, her eyes glowing as her horn flashed a bright light. "Did you think you could just get rid of me that easy. You fools, you will all die now."
She rose to the highest point in the room and everything became a searing light that began to burn their skin, making them wail with cries of pain. Suddenly everything went dark. Celestias light extinguishing as fast as it had come. The mare began falling to the floor in a spiral. Finally crashing as she stared at the shadow in the middle of the room.
"H-how," was the only thing she asked.
"I drained your energy," it said, "and now, it's time for you to go."
The shadow walked towards her, ignoring her pleas for forgiveness and screams of mercy. It rose to it's hind legs and spread it's two front hooves towards the sky as he gazed upon the Princess. The princess's cries began to die away and fade into wimpers untill suddenly everything stopped. The shadow hunched over and seemed to shrink on itself, curling into a ball as it shriveled up and dissapeared, never to be seen again.
The princess of the day rose up once more, slowly, but surely. She walked over to her younger sister and touched her horn to the younger princess's, sealing her fate and sending her to the Moon.
She walked over to the Dragonequius and began to turn him to stone from the feet up. He gave her one last pleading look before his head became encovered in stone and he managed out, "Please, go easy on Chrysalis."
The princess only nodded and finished the job, turning slowly to the last living being in the room besides herself. She used her horn to levitate the figure and contemplated what to do, deciding on banishing her to the outer kingdoms after a few minutes of thought. She used her last bit of magic to heal the broken bones and teleported her to another kingdom far away.
She collapsed on the throne room floor and cried. She wept because she had lost her one and only sister, even if the things she had been accused of were true, it had hurt. She had taken the kingdom, forced Sombra into a prison and locked him there, deciding on a cover story, should he ever get out.
She looked up at the Moon through one of the glass panes and said, "I'll love you forever and always Luna, no matter what happens." She made a mental note to look up the memory spell she had used and then gave up, opting to lay on the floor in the throne room the rest of the night.