I'm really sorry, but...
Rainbow Dash awoke in the middle of the night. She didn't know what had woken her up, so she listened to the silence around her. Wind howled around her cloud house and she could hear the creaking of wood, as said wind moved the house. The shadows in her room seemed to dance around her bed, like they celebrated an ancient ritual about to be made.
Her mind wandered back to the creaking. Something was off. Then it suddenly hit her; if her house was made out of clouds, how could she hear the wood creaking?
Slowly she stood up from her bed and snuck over to the light switch, her body covered in cold sweat. As the crystals bathed the room in their white light she saw Pinkie Pie.
The pink party pony was standing by her bed, staring at where she had been mere seconds ago. With the new light she was able to see Rainbow Dash and her fluffy hair wiggled around when her head turned.
"Hello, Dashie," she said happily but not without a sad undertone.
Dash gulped and tried to smile, "Hey Pinkie, what are you doing in my room?"
Pinkie Pie frowned, "You know, I'm really sorry, but," - she pulled out a large butcher knife - "I have to kill you." She made a few steps towards Rainbow.
The pegasus' eyes widened and she darted towards the door. The door shut with a loud bang in front of her so she turned to fly out of the windows. Where the windows had been previously, there was now nothing. She looked back at her friend, who looked sincerely sad. "I'm really really sorry, Dashie. There is no way out of it and it has to happen."
She jumped towards the pegasus. Dash was stunned and only noticed the blade in her heart a few moments later. It did not hurt, rather there was a strange coldness spreading through her. She looked at Pinkie her eyes pleading for an answer to this betrayal, "Why?"
"I wish it would be me that had to die and I am really sorry," said Pinkie Pie with tears in her eyes, "but it has to happen."
Rarity woke up when someone knocked at her door. Groaning she stood up from her bed and went to look who it was. When she opened the door she saw Pinkie standing outside. Tears flowed over her face and she sobbed almost inaudibly.
"Pinkie, darling, what is wrong? Come in. Can I offer you some tea?" asked the unicorn politely. She offered the pink pony a seat on her couch before she went to the kitchen and made a strong tea.
When she returned to the living room Pinkie Pie hadn't moved at all. She sat exactly the same way as before. She filled the tea in two cups, one for her and one for Pinkie Pie.
"Thanks," whispered the pink mare and took a sip, "The tea is great."
"What is bothering you, darling?" asked Rarity. She had removed most of the beauty products she used during the night, although she still had a light case of bedmane.
Pinkie took a deep breath, "I killed Dashie. I stabbed her right in the heart."
Rarity stopped breathing for a moment, "If this is a joke of some sort..."
"It is not," interrrupted Pinkie absolutely calm, "I took a butcher knife and killed her. But that is not the worst part."
"W- what is the worst part?" stuttered Rarity.
"I'm really sorry, but," she said and grabbed something behind her back, "I have to kill you." She pulled out a butcher knife that was covered with red blood, still dripping.
Fear took over Rarity's mind and her instincts kicked in. She darted towards the door only to find it closed and locked. She turned around and found Pinkie standing right behind her. With eyes widened by fear she stared at her friend.
"I'm really sorry, Rarity," said Pinkie Pie before she stabbed Rarity in the stomach. She pulled the knife out and stabbed her friend again. And again. She stabbed her friend over and over, even after her body had stopped moving long ago and her sobs weren't interrupted by the screams of pain from her friend.
She continued to sob for a few minutes before she walked out of the room, the door now unlocked again.
Applejack woke up in the middle of the night. It was hot in her room and her throat was dry as the desert. She stood up and made her way to the kitchen. She grabbed one glass out of the cabinets and filled it. After a few gulps she cleaned the glass and put it back.
When she turned around she stared directly into the eyes of Pinkie Pie. She jumped back at her sudden appearance, "Whoa, Pinkie ya gave me one hell of a scare. Ya okay there?"
Pinkie shook her head, "No, not really."
Applejack's eyes softened and she gave Pinkie Pie a hug, "Whatever it is, Am here to help y'all, sugarcube."
"That is exactly my problem, Applejack. I'm really sorry, but," - Applejack felt a stinging sensation in her neck - "I have to kill you."
Applejack wanted to pull away from the hug to look Pinkie in the eyes but she couldn't move. Her body didn't respond to her anymore. Pinkie let go of her and she fell to the ground, unable to move any limbs. On the ground before her gathered a pool of blood. She wanted to speak but only blood left her mouth. In her fading vision she saw Pinkie Pie leaving the room.
Before she was fully gone she turned around, "You know, it get's easier to accept. I'm really sorry, but it has to happen." Pinkie Pie turned her back to her dying friend and left the house.
Outside she sighed, "I really wish it wouldn't have to happen." With the sound of a balloon deflating, her mane became limp and lifeless.
Fluttershy woke up to the feeling of something moving across her throat. She opened her eyes to see Pinkie Pie standing above her, holding a large kitchen knife in her hoof.
"I'm really sorry, Fluttershy, but," she began. Fluttershy wanted to ask what had happened but only a gagging sound came out of her mouth and she tasted blood.
"I have killed you." Fluttershy lifted her hoof to her throat and felt something wet. She moved her hoof up and saw it covered in blood. She wanted to gasp but only blood filled her lungs. She looked at the pony above her, surprised by the betrayal of her friend. The face of the pink pony was completely emotionless. She felt her life flowing out of her, as her heart pumped blood out of her body with each beat. Her vision faded to darkness.
Pinkie looked at the motionless body of her friend. Blood still flowed out of her sliced throat, slowly because there was no heartbeat anymore. The mattress was soaked with blood when Pinkie finally left the cottage at the outskirts of ponyville. She turned towards the library in which her last living friend was.
Twilight Sparkle woke up when someone loudly banged on her door. Still half asleep, she stumbled down the stairs carefully, hoping not to wake up Spike. She opened the door and saw Pinkie Pie standing on the doormat. Her hair was limp and lifeless and a few red stains were on her coat. "Can I come in?" she asked. Her voice was emotionless and dry.
"Yes. I'll make you a cup of hot chocolate, okay?" said Twilight, trying to sound as calming as possible. She helped Pinkie on one of the chairs in the kitchen and began to heat the milk with her magic. A few minutes later a steaming cup of hot chocolate stood before Pinkie Pie, who took a few sips out of it.
"Pinkie, I'm no expert but I can see that something is bothering you. What happened?" she asked friendly.
Pinkie took a sip from her cup before answering, "I killed the other elements, Twilight, we are the only two left." She shivered slightly.
Twilight's ears laid flat against her head, "I'm sure that was just a bad dream, Pinkie. Just a nightmare produced by your subconscious."
"I sliced Fluttershy's throat, so she wouldn't have to feel any pain," Pinkie said bluntly, "She was dead before she really knew what had happened."
"But why would you do something like this?" asked Twilight.
"Because he demands it. He said that I have to kill the other elements and I have to eliminate all witnesses," explained the pink pony, "and I'm really sorry, but," - she pulled out a large knife out of nowhere - "I have to kill you."
Twilight was stunned by this for a second. After she had overcome her mental stupor she bolted for the stairs. Before she even knew what had happened she had run directly into Pinkie's knife.
"He can alter the reality around us, you never stood a chance, Twilight. I have no choice. I'm really sorry," the pink mare apologized, "but Spike heard us."
She left her dying friend behind and trotted up the stairs. When she entered the bedroom the small baby dragon laid in his bed and pretended to be asleep. His shivering body betrayed him.
Before the drake could react she had rammed her knife through his closed eyes into his brain. His body jerked once and then laid dead in his basket.
Pinkie stood above the dead body of her purple friend. She screamed her pain into the world but her cries for help remained unheard. If she could, she would kill herself. But her job was not finished yet.
"You know the rules," she said between her sobs into the empty room, "I can't leave any witnesses alive." She clamed down visibly, her body relaxing and her mind focusing on the task.
"I'm really sorry, but," she looks you directly into the eyes, "I have to kill you."