A/N: Hey so here comes the fourth chapter of Serenity, just for clarity the concept of Serenity, the colour, nane, cutie mark and habits before we found out she was Nightmare Rarity is completely mine. Please Read & Review it really does help me.

Enjoy ; )

Luna took over her duties for the night. She made her rounds through the castle making sure it was at peace, she greeted the guards after every entrance she passed. She went into the throne room and sat on her own, she then called for her royal guard, they came immediately to their princess. She asked her head guard to answer for them all, she proceeded, "Where do your allegiances lie?" "With you Princess Luna," answered the guard. Luna nodded and asked, "How far would you go for your Princess?" the guard answered "We would die for them," Luna became annoyed and said, "I didn't say Princesses I said Princess." "So let me ask again how far would you go for your Princess." The guard answered "We would die for you Princess Luna," "Good and would you trust her decisions?" asked Luna, the guard answered "Without question your highness." Luna walked over to her Royal Guard and touched the head guard with her horn, he began to transform, his height increased slightly, his armour turned black and his eyes became black with a moon light white slit for his pupil. After his transformation he looked stronger in every way, the other two took to the transformation with open minds, they also wanted to be stronger than the other guards of the castle. From nowhere the Shadowbolts appeared behind the guards, Luna smirked and asked speaking very clearly, "Where do your allegiances lie?" They all answered in unison, "With our Queen." Luna began to cackle like her darker self.

Rarity went to the cafe with Rainbow Dash, who had sprained her wing during her exercises and had nothing better to do. "Wow Rarity I didn't think you could get so mad," Rarity sighed and asked, "Rainbow Dash, how would you feel if she sold something so precious to you to get that jacket?" Rainbow Dash shrugged and said, "I don't know, I guess I would be pretty mad but I would just let it blow over." Rarity rolled her eyes and then asked, "And if that item put you heavily into debt?" Rainbow Dash then said, "Oh well, it's just a thing, I would value my family more than something." Rarity looked at her and then said, "You know Rainbow Dash you're right, I need to make things right with Serenity, I just hope I can find her in the Everfree forest." "I'll help you, after all she's my friend and I really like this jacket." said Rainbow Dash, she hadn't taken off that jacket since Hearth's Warming Eve.

They headed into the Everfree forest together in search of Serenity. Serenity woke up in a meadow in the Everfree Forest she didn't know where she was in the fact of how far she was from any civilisation, suddenly she remembered, she was possessed by a Nightmare, she didn't remember what happened during those years after the mental institution, but she did remember the harsh things Rarity had said, she saw she was wearing her favourite black jacket. She then knew what she had to do, she decided to head back in the general direction.

Rarity and Rainbow Dash were searching for Serenity, calling her name hoping that if she was near enough she would hear them. "Oh Rainbow Dash I hope we find her, I'm afraid she'll hurt herself," said Rarity, Dash nudged her shoulder with her elbow and said, "Don't worry Rarity, she seems pretty clever, I'm sure she wouldn't get hurt." Rarity kept walking and said, "I don't mean it like that," Rainbow Dash said realising what she meant "Oh." They continued their search for Serenity.

Serenity sighed and said, "I have no idea where I'm going," she kept walking not looking where she was stepping and tripped on a stone spraining her rear right ankle, she exclaimed in pain, "S#!t that really hurt." She knew she couldn't walk with her ankle now, she sighed and said, "Maybe it's for the best, if I get eaten there'll be a few positives; one: I'll feed an animal. Two: Rarity won't see me again and three: I'll be dead and bother nopony anymore." she lied down on her back awaiting her death, then she heard her name, she sat up, "Huh?" she listened again, she heard Rainbow Dash of that she was certain, then a second voice, her eyes widened, Rarity. She called out, "Help! Help! I'm over here!" suddenly within a few minutes Rainbow Dash came through the trees and said, "Here she is I've got her." shortly after that Rarity came through the trees and hugged Serenity and said crying, "I'm so sorry Serenity, I didn't mean to say all those harsh things about you I was just angry please forgive me," Serenity burst into tears and said, "I'm sorry too I didn't know what had gotten over me I knew you treasured that topper," Rarity shook her head and said, "I don't care anymore about that stupid topper all I care about right now is you."

Rarity stood up and tried to help up Serenity who exclaimed in pain, "OW!" she had forgotten her ankle was sprained, Rainbow Dash took notice and went to get sticks and vines to make a splint, she was very capable in the forest, somehow she knew first aid for these type of situations. She splinted Serenity's ankle and the three slowly made their way back towards Ponyville, when they reached the outskirts of the small village Serenity asked to stop at the shop just near the the forest, they entered and Serenity limped over to the counter and said, "Miss Serenity." The owner smiled and said "Fortunately nobody was able to buy it." She used her magic and gave Rarity her crystal tree topper back to her. Rarity looked at her and asked, "Why? I thought that you would keep the money?" Serenity nodded and said, "Yes, but the receipt says if it isn't able to sell then they'd give it back to me and I would still keep the money." Rarity then decided that they should go to Twilight and ask about Serenity's ankle.

Shortly afterwards they arrived at Twilight's door which opened with a deep pink magic aura around it. Rarity smiled and said, "You got your magic back," Twilight nodded and said, "I just can't explain it, yesterday I didn't have magic and now I do." Rarity was happy that her friend got her magic back then asked her, "Could you look at Serenity's ankle, she sprained it in the Everfree forest a few hours ago," Twilight used her magic and after that Serenity's ankle was fine. Serenity then said, "I can't remember anything from after my years in the mental institution or Hearth's Warming Eve." Twilight looked at her and asked, "Is there anything you wish to tell us?" Serenity sighed and said, "I was possessed by a Nightmare." the room fell silent, a heaviness fell onto the room. "What do you mean?" asked Rainbow Dash, Serenity began, "When my parents left me in the mental institution in Manehatten they abandoned me there. I felt so sad... then I can't remember," Twilight walked over and said, "Let me try something," her horn glowed around Serenity's head, who instantly began to remember something, "I remember me being there for fifteen years, I thought I was alone, then I met a strange pony. I can't remember her voice, but she had a purple and white mane, she was quite tall for a pony in fact taller than Princess Celestia, she was black, her mane also had stars in it. I couldn't see her cutie mark though, her horn had some sort of crown in front of it, but it was the length of Princess Celestia's as well." Rarity looked away and said, "That is me Serenity, well my darker self." Serenity looked at her confused.

Twilight explained, "You see Serenity, Rarity is speaking about Nightmare Rarity, it was back when she was afraid that she would be replaced by another more generous pony, so she fell into darkness only because she was manipulated by the shadow beasts of the moon."

Serenity nodded and continued, "I was interested in this pony and wanted to befriend her so I tried to and after a few months we became friends. If I knew she was what Rarity once was then I wouldn't have befriended her and then I can't remember. Soon after I was released and don't remember much from that either." Twilight said, "That must have been when she possessed you. Can you remember anything else?" Serenity shook her head, "The last thing I remember was the harsh things Rarity said, but she apologised for it otherwise I can't remember anything." Twilight didn't know what to do, but she knew who they could go to. She told the others to get ready to depart for Canterlot, she knew that if anypony could explain what was going on Celestia would. A few hours later at dusk they departed for Canterlot on the last train for the day, the train ride was luckily short because there weren't many ponies on the train travelling to Canterlot. They arrived just as the moon was raised, they headed for the castle, they reached the castle gates easily. Suddenly the guards halted them, Phalanx the head guard that had replaced Shining Armour stood before them and said, "Who dares to enter the castle without permission," Twilight looked up to him and said, "Twilight Sparkle the Magical, Rainbow Dash the Loyal, Rarity the Generous and her cousin." Phalanx recognised the names and said, "My apologies Princess Twilight we have been on edge lately since Princess Luna's Royal Guard have gone missing for some time now."

Twilight and the others walked into the castle looking for Celestia, the first place they looked was in the Dining Room, and sure enough she was having dinner alone. Celestia looked up and smiled, "Twilight my dear student, Rainbow Dash the Loyal, Rarity the Generous and a pony I have not yet met it seems." They walked over to her and took seats at the table, Celestia looked at Serenity and asked, "Who might you be?" Serenity swallowed and said, "I'm Serenity your highness, Rarity's cousin." Celestia smiled and said, "Well it's always a pleasure to meet relatives of Rarity, I like your mane style it's very nice." Serenity blushed slightly at the compliment from the Princess. Celestia turned to Twilight and asked, "So have you figured out why your magical abilities are gone?" Twilight shook her head and said, "Actually they're back today," Celestia lifted an eyebrow and used her magic to check, she was astounded, "I can't believe it, it seems whatever dark magic was upon you has disappeared completely." Twilight then asked, "Can we head to your study? We have something to tell you." Celestia nodded and they headed to her study. Twilight sat across from Celestia, her friends sat next to her, Twilight continued, "We have reason to believe that Nightmare Rarity has returned," Celestia looked at her and asked, "Are you sure? What evidence do you have?" Rarity answered, "Serenity met her in the Manehatten mental institution you highness, and she says she was possessed because she couldn't remember much after that or after Hearth Warming's Eve." Celestia used her magic to check Serenity.

Celestia said to them, "I can't sense anything right now, if she was possessed I would have sensed it in her." Serenity then asked, "What about Luna, could she have sensed it?" Celestia answered, "Yes she can, but why do you ask?" Serenity answered, "We met on Nightmare Night last year." Celestia asked one of her guards to retrieve Luna, she stepped into the room and asked, "What was it you wanted to ask me Tia?"

Celestia motioned for her to sit next to her at the table in the study, then proceeded to ask as soon as she had sat down, "Did you sense anything strange about Serenity when you met her on Nightmare Night last year?" Luna looked at Serenity and said, "No not at all, why?" Celestia explained, "She claims to have been possessed by Nightmare Rarity for quite sometime," Luna looked back at her and said, "Sorry Tia I didn't sense any Nightmare within her, after all I was helping Rarity with her nightmares before I was banished to the moon." She clasped her hooves around her mouth. They looked at her, she then said, "Did I say banish? I meant went to the moon to sort out somethings," she then giggled nervously.

Celestia looked at her sister intently, she turned away nervously, "Luna will you look me the eyes when I have something important to say to you." Luna turned slowly around and looked into her sister's eyes, Celestia stared into her eyes, Luna blinked and Celestia saw that her pupil changed into a slit and back to a normal pupil again. Celestia asked, "What exactly did you do on the moon Luna?" Luna began to stand up saying nervously, "Oh wow look at the time... I guess it's time to lower the moon and make way for the dawn... hehehe," Celestia locked the door with her magic, also making sure it was magic proof. She proceeded, "Do you want to tell us something sister?" she motioned for Twilight, Dash, Rarity and Serenity to get behind her as she stood up.

"So Luna tell me what did you exactly do during your visit to the moon," Luna tried to open the door, she resorted to using her magic, she looked at Celestia saying, "Tia please let me out, I need to lower the moon to make way for your gorgeous day," Celestia smiled and said, "Nice try." Luna sighed and suddenly shot Celestia with the others out of the study window. Celestia hit the ground she caught the other four with her magic and gently set them on the ground, she looked at the hole where the study window was. Luna glided down and said, "I'm sorry Tia but you forced my hoof." Celestia stood up and said, "You don't have the right to call me that Nightmare Moon," Luna sighed and said, "Well it looks like the jig is up." Suddenly the wind blew from Luna. Her eyes began to shine white as she began to transform, she gained in height, matching her sister's, her coat became black, her wings changed shape, armour was on her body, she opened her eye, her pupil becoming a slit. She had become who she really was on the inside Nightmare Moon, Celestia spoke, "Luna you are better than this, you don't have to feel jealousy anymore." Nightmare Moon chuckled and stated, "You think this is about jealousy? No, it's about power and I want to be the ruler of Equestria by myself." She began to cackle and she vanished into a blue mist.

Celestia grew sad as she realised that her sister was gone and replaced by Nightmare Moon.

She looked towards the ponies looking at her with concern, Celestia sighed and said, "Come with me little ponies, we are all hurt, let's get to the medical wing of the castle." They reached the front gate and Phalanx ran over to Celestia and asked, "Princess Celestia are you alright? What happened? Where is Princess Luna?" Celestia groaned in pain and said, "Send out the pegasus guards to search for Nightmare Moon, she's returned, we need to find her before she reeks havoc on Equestria," Phalanx nodded and went to the tower where the pegasus guards were stationed. Celestia and the other four ponies limped to the medical wing of the castle, Rainbow Dash was at the very back and she took the brunt of the force, her head above her right eye was cut open from the glass. Twilight was right behind Celestia when Luna fired, not all of the magic beam hit Celestia she was hit in the side, so she felt great pain in her right side of her abdomen, the flesh was torn badly she needed stitches. Rarity had suffered two cracked ribs when she hit the metal frame of the window.

Celestia was hit in the chest by the magic beam, it wasn't meant to kill just hit her hard. She felt short of breath, she also knocked her head on the wall where the top of the window was situated, so she had a splitting headache. The nurse ponies tended to them, stitching Twilight, resetting Rainbow Dash's wing and bandaging her head, wrapped up Rarity's chest for her ribs and giving an ice pack for Celestia's head and sorting out her chest so she could breath again. Rarity asked the nurse tending to her, "Where's Serenity?" The nurse pony finished bandaging her and looked to the direction of an unconscious pony on one of the beds. Unfortunately Serenity had taken the worst injuries, despite being in front of Rainbow Dash when Luna fired her magic beam. When they were shot at, Serenity had hit the window sill with her hip, causing her to tumble in the air and hit one of the horizontal metal frames with her neck and a brick hit her right in the right half of her face causing a massive bruise. Rarity hobbled over to her cousin saying, "Oh Serenity I'm so sorry, this should not have happened to you." She lowered her head in sadness. Rainbow Dash stood up and put a hoof around her friend, "Don't beat yourself up about this Rarity, it wasn't your fault."

Celestia walked over with Twilight and said, "Rarity we need to get her to the Canterlot hospital, we do not have the equipment to support her if her condition takes a turn for the worst." Rarity nodded and allowed the nurse ponies to take Serenity to a carriage where they took her to Canterlot hospital, Rarity's contact details were already with the hospital because she and Fluttershy were out and a carriage ran over one of Fluttershy's legs, so if anything did happen she would be informed. Celestia lowered the moon and raised the sun to beging the day, she was in her study when Phalanx came in and said, "Your majesty the Pegasus Guards have returned, they have not seen any sight of Nightmare Moon all night." Celestia sighed and said, "Thank you Phalanx, tell them to get some rest I might need them to search again tonight." Phalanx nodded and left the study, Celestia put her hoof between her eyes and sighed, "We need to find her before it's too late." Rarity, Twilight and Rainbow Dash had been given a room to share while they recovered from their injuries, Twilight had sent off a letter to Spike to tell the others to get to Canterlot, so she could explain why they weren't in Ponyville. A few hours later the other three came to the castle and were directed to where they were staying, hugs were exchanged between the friends, Twilight then began to explain, "We came here because Serenity had said she was possessed by Nightmare Rarity, when she was checked by Celestia she said she sensed nothing. Serenity mentioned meeting Luna at Nightmare Night, so Celestia asked her if she sensed anything, but she said she hadn't, it turns out that it was actually Nightmare Moon."

She then told them of Serenity being admitted into the hospital. "Well that sucks a load of hay," said Applejack, Rainbow Dash agreed with that statement to the full extent, Flutershy asked, "So what is Celestia doing about all of this?" Twilight shook her head, "To be honest Fluttershy I don't know, I think she's just trying to work out a plan or something." A knock on the door was heard and a guard poked his head through the slightly open door and said, "Princess Celestia would like to see you all now," Twilight thanked the guard and he closed the door, the six friends went to Celestia's study and sat at the table. The friends saw where the hole was as the window had not been repaired, Celestia looked at them all and sighed, "Unfortunately we cannot find her, if we knew where she was we would be able to figure out a plan. Tonight I shall send out the Pegasus guards again to search for any mention of her, but for now I ask for you all to stay here in Canterlot if we need your help." Twilight and her friends agreed to stay for as long as they could.

Rarity was in her room when there was a knock on the door, she answered it and behind it was a guard who said, "Forgive me for disturbing you but this letter is for you." Rarity thanked the guard and took the letter, she saw it was from Canterlot hospital. She opened it and she read it, immediately the letter dropped to the ground from her magic, she then collapsed onto the ground. Her vision was clear but her hearing was slightly gone, she could see Rainbow Dash running towards her, she heard the muffled voice of her friend in distress, "Rarity? Rarity! Come on don't do this," Suddenly she saw Celestia and the others walk in, she blinked like normal, but didn't respond to anything. She saw the nurse ponies from the medical wing of the castle come towards her, then she blacked out. She awoke in a bed in the hospital wing of the castle, she looked to her side and saw her friends standing around her, she asked, "What happened?" Twilight answered, "You went into shock after reading a letter from Canterlot hospital, you were out for over two days." Rarity then remembered what she read, "Dear Miss Rarity, unfortunately your cousin Serenity has slipped into a severe coma, we will keep her on life support for the time being, however as her legal guardian you will have the decision of taking her off life support or keep her going until she shows any sign of improvement, please come by to receive more details. Signed: Hospital Administrator."

Rarity decided to head over to the hospital to see Serenity, when she entered she headed over to the front desk. "I would like to see Serenity please," the nurse nodded and lead Rarity to her cousin's room. Rarity walked in and saw her cousin Serenity hooked up with multiple wires leading into multiple machines, she walked over to the side of the bed and immediately began to cry, "Oh Serenity... I will avenge you... I promise..." Rarity knew what she wanted to do, kill Nightmare Moon for doing this to her. She left the hospital with a new state of mind, she returned to the castle and went to the Pegasus Guard tower, she woke up the head guard who asked after being rudely awoken, "Who asks for our services," Rarity grabbed him by his armour and said, "Now you listen to me, Nightmare Moon is out there and I need to find her, don't come back until you've found something that will lead me to her." The guard didn't argue and assembled the rest of the force to fly out and search for Nightmare Moon, Rarity stood on her bedroom balcony and watched as the Pegasi began to fade into little dots over the horizon.

At dinner Celestia asked, "So how is Serenity?" Rarity glared at her, "Well how do you think she is doing? If you weren't so blind you would actually care about my cousin, but no you're only asking in an attempt to make me feel better about myself, after all what should I expect from somepony who has everything, you have no idea how I feel right now." Twilight's eyes widened, Celestia stood up, "You're wrong of course I know how you feel, how do you think I sleep at night knowing that my little Luna is out there right now somewhere being held captive by Nightmare Moon and..." "Oh give me a break, I'd expect somepony with eyes as big as yours to at least see the fact that Princess Luna is nothing more than a selfish little b!***h who cares for nopony but herself and her stupid nights." Celestia was pushed over the edge at that moment, "HOW DARE YOU! IF IT WERE NOT FOR LUNA YOU WOULD STILL HAVE NIGHTMARES! IF IT WERE NOT FOR LUNA YOU WOULD'VE BEEN NOTHING BUT A RUNDOWN DESIGNER! IF IT WERE NOT FOR LUNA YOU WOULD STILL BE NIGHTMARE RARITY!" The others had never seen Celestia like that before, she even used the Royal Canterlot voice which she hardly ever used.

A/N: So there you have it the fourth chapter of Serenity hope you enjoyed it, please read and review it helps me a lot to continue to write these stories, but even if you don't I will continue to write anyway you shall never stop me.