The Great and Envious Trixie
Author's Note
Sorry about the tags. Couldn't think of the proper ones to add, so I put in the basic ones. Sorry if it confused you. 
Chapter 1: Discovery
Three girls leaned over the railing on the deserted second floor. "When are we going to do something?! We've been watching her for weeks!" One whined.
"Shh, Sonata!" Another hissed. A blue skinned girl on the first floor appeared to be having some difficulty opening her locker. She was the only one in the hall.
"Oh no! I'm going to be so late!" She murmured, briefly glancing at the overhead clock. Sonata looked like she would burst. Adagio raised a hand and jumped over the railing. Aria and Sonata quickly followed. Trixie heard a loud thud and spun around.
"You are t-the..." Trixie stuttered but was too shocked to finish her sentence.
"The Dazzlings, yes. But do not be alarmed, we are here to help!" Adagio tried to sound as friendly as possible.
Aria nodded, stepping forward. "We are going to assist you in your revenge plans."
Trixie was frozen, but managed to say a few words. "Revenge? On who?" She asked.
"Sunset Shimmer, who else?! We're going to help make her pay! For a small price of course!" Sonata chirped, pointing at her bare neck.
"Sunset Shimmer..." Trixie echoed. She couldn't deny her hatred for Sunset Shimmer. She was the bad guy and she got power, but Trixie was left with nothing. "But your pendants, they were destroyed." She replied.
"But you can fix them, it isn't impossible. After all, you are the great Trixie Lulamoon..." Adagio turned to the other Dazzlings, who nodded.
"Well, if you insist... I guess I could try making your pendants. And expect only the very best magic from the great Trixie Lulamoon!" She boasted, even though she didn't know a thing about magic, let alone Siren magic.
"So do we have a deal?" Adagio held out her hand, grinning from ear to ear.
"Yes!" Trixie exclaimed shaking her hand, not needing anymore persuasion.
"Now, we wouldn't want you to be late for class..." As Adagio said that, Aria walked up to Trixie's locker and opened it with little effort. "Meet us in the library at midnight. Ta-ta for now!" They walked off. Trixie stood there with her mouth gaping for a moment. She had just met the sirens, whom she thought had been sent back to wherever they came from.
A smirk made its way onto her lips. "Watch out Sunset Shimmer, I will have my revenge."
The bell rang, students were filing out of the school. Trixie was eyeing Sunset Shimmer from behind. "Just you wait, Sunset Shimmer." She murmured to herself. She had finished one tiring but thrilling day.
She ran off to the nearest Jewelry store, hoping to be there before it was closing time. Luckily, it was not. She rushed in and pressed her face to the glass, looking for the perfect pendants to buy. She gasped, right there in the middle, were the exact same necklaces the Dazzlings used to wear. She then looked up at the store keeper and pointed to them. "I want these ones." She demanded. "How much?"
The store keeper gazed back at her, shocked. "You want these necklaces?" She asked, bewildered. Trixie nodded. "These are the ones that some evil magical things used to wear! It all went down on Canterlot high..."
The store keeper was about to recite the story she had heard before being shushed by Trixie. "I know, I heard from... Someone! Now tell me, how much?" She raised her voice a little.
"It's free. I just want to get rid of these things! I don't want anything that might be linked to those wicked things!" The store keeper exclaimed, grabbing the pendants and handing to Trixie. "We fixed them up a bit, but nobody wants to buy it." She explained.
Trixie nodded, catching sight of a blue amulet. She decided to buy something for herself as well. "I would also like that please." She said, pointing at it.
"Sure, but that isn't free. It's 20 dollars." The store keeper held out her hand and Trixie put some money in her palm. "Nice doing business with you!" She pointed at the door. Trixie turned and walked out.
Trixie put on a black hoodie, which ever since the events of the Battle of the Bands had become her usual attire. She didn't want to be noticed sneaking onto school grounds. She walked to the back of the school after checking if the coast was clear. She had very strategically picked her point of entry, this window was the one incapable of moving, neither up nor down, and she had found a way of opening it mere days ago. She took a skinny but strong branch hidden behind a bush and slid some of it through the small opening, she forced all of her weight onto the other half, which managed to get the window up halfway. Trixie threw the branch back into the bush and crawled through the opening. Now, she had to occupy herself until midnight. She crept along the empty hallways, knowing that the school wouldn't officially empty out until 6 Pm. She entered the laboratory, removing the three pendants from her pocket and placing it on the desk. She threw on a lab coat with goggles and got to work. She experimented with the chemicals to try to pinpoint the Equestrian magical force.
She poured some of her final product into a measuring cup. Then she carefully dipped the pendants into it. When she removed them from the bubbling concoction, they had a red aura surrounding them. They were almost complete, but she wanted to give the Dazzlings the best in exchange for revenge, not just half the effort. It had taken her hours, it was half past 9 now. She could feel that the pendants weren't at their full potential. Then it hit her. They needed hatred to jump start them. "I hate Sunset Shimmer... Hate... Hate... Hate! Argh!" She shoved most of the tubes and containers off of the table in a fit of rage. "Hate!" She shrieked, the necklaces only strengthened her jealousy of Sunset Shimmer. "You get all of the magic but I don't! You're still the evil demon we all knew! You haven't changed at all!" The necklaces were now glowing red. Trixie continued screaming at no one in particular until 10 Pm, when she fell asleep, exhausted.
Midnight. Trixie was awoken by the glowing pendants, which let out soft beeps. "So you're also timers? Interesting." She commented, grabbing them.
She made her way down the dark hallways. She slowly pushed the library door open to reveal three Sirens waiting for her. "We were wondering when you would get here." The necklaces levitated from Trixie to the trio. "Thank you, we'll make great use of these..."