I: She'd Dreamed This Dream as Days Gone by...
She had dreamed this same dream as days passed. When she kept her hopes high, when life was worth living to her, the dream wasn't as painful.
But now it was.
A majestic, lavender alicorn and a green and purple dragon stood before five graves. Each on had a cutie mark on it. (From left to right) Three balloons, three butterflies, three gemstones, a lightning bolt from a cloud, and three apples. It was raining currently which concealed the tears that the alicorn wept.
The dragon put his arm on the alicorn's back, and he gave a small squeeze. The alicorn sniffled.
"Please, don't leave," the alicorn whispered. "I can't be alone. Please, don't leave, Spike."
The tears began to stream down her face faster.
"Shh, shhh," Spike, the dragon, replied. "I won't."
"Thank you..."
She turned towards Spike to hug him, but she was met by the skeleton of Spike. The skeleton collapsed at the alicorn's hooves.
"Sp-Spike?" The alicorn closed her eyes and gritted her teeth. More tears were about to stream down her face when-
"Cease this horror!!!"
Darkness suddenly filled the dream, and at the center, was a gray stallion with an etheral, black mane and tail, and curved horn dipped red, and piercing, red, dragon eyes. He smiled revealing a set of carnivorous teeth meant for sucking blood and ripping apart meat.
"Hello, Twilight Sparkle."
The lavender alicorn, Twilight Sparkle, widened her eyes. "S-s-sa... B-but you're dead! You have to be! The Crystal Heart destroyed you!"
The stallion laughed manically. "That is what you thought! But my horn survived. With my horn, I can regenerate. It astounds me on how somepony as smart and curious as you would've discovered this spell, or, at least, you recreate the spell yourself."
Twilight charged her horn ablaze with a rainbow aura. She blinked, but when she opened her eyes, they were pure white. "Leave now, Sombra. You are trespassing on the Princess of Friendship and Magic's mind. LEAVE!!"
Sombra raised an eyebrow. "Before I remove myself from your mind, may I offer a deal?"
Twilight gave her magic a small amount of slack. Her horn stayed lit, but her yes had returned to normal. "What," she spat.
Sombra grinned. "I, Twilight Sparkle, can give you something that you don't have. And if you accept this deal of mine, I can give it to you."
"What," she growled, wanting this dream... no, nightmare... this nightmare to end.
His smug grin disappeared. "Alright, Princess, be that way. My offer is..." His grin returned. With a flick of his hoof, a obsidian tiara appeared with a magenta diamond. "... to give you all magic. If, you accept me as a mentor."
Twilight was taken aback. She tapped her chin in thought. "All magic... But... But I can't abandon Equestria! And this is all a trick, isn't it!?" She flared her wings, her horn blazed brighter, and the light returned to her eyes. "I will not fall for it, Sombra. Now, Leave."
Sombra let his grin fade. He growled and melted into the dream, vanishing completely.
But the crown had not disappear.
Twilight scanned the crown. It seemed harmless, even after a few a Scan Spells.
Eventually and unfortunately, her scientific curiosity got the best of her. She poked it.
Suddenly, she felt so much power surging through her blood and mind.
Light magic. Dark magic. Midnight magic. Dawn magic. Day magic. Dusk magic.
Universal magic.
She felt it all surging in her, her magic, and her blood.
Twilight's eyes turned midnight black. Her pink highlight turned a sickly green. She screamed in pain as her teeth sharpened and formed fangs. Her horn lengthened. Parts of her wings became darkness itself. Her cutie mark morphed from magenta to midnight black.
She felt something rumble in her throat. When she let it loose, it was a loud, happy, yet evil laugh.
And it felt fantastic.
Twilight Sparkle paced back in forth in a new dream, waiting for certain gray stallion with a curved horn.
"I see you've been waiting."
Twilight galloped to the sound and nuzzled the physical object she came in contact with.
"You dare to touch a king!!!??!"
Twilight's ears wilted under the gray stallion's angry glare. "Sorry, Sombra..."
Sombra snorted. "You should be thankful that I'm forgiving you so easily. If you were one of slaves, I would've whipped you until I saw your bones beneath your flesh!"
Twilight widened her eyes in disbelief. "Fwa... What!? How could you be so cruel!?"
"Ha! A ruler must be cruel to have true authority! But do not worry, Twilight..." Sombra took on a regal position. "... I will teach you what you need to be a ruler, my protege."
Twilight Sparkle began flying towards the Castle of the Two Sisters at twilight, the destination and time where Sombra wanted to teach her.
Her mane and tail was unnaturally flowing. Her highlights sparkled their colors like glitter. Her hooves were covered by platinum slippers, and her chest was adorned with simple, platinum chest piece. On her head behind her long horn, a small, platinum tiara sparkled. Her majestic wings rustled as the wind went underneath them.
Twilight zipped over the ever expanding Everfree. After these 1,376 years, it had expanded about the size of Twilight's original Ponyville.
Then, she saw the castle.
Ponies had cleared a lot of room around it, and it was now a "must-see-landmark" for tourists. Fortunately for her and Sombra, it closed after sunset.
Twilight adjusted her wings and began to glide down to the castle. She tilted her body so she circled the castle while descending.
She smiled, and a tear fell as she recalled all the renovations that Rarity had made. The scrubbing of the walls and floors. The recreations of tapestries. The tuning of the organ, now known as "Pinkie's Organ" for the tour. The refurbishing of the Two Sister's original bedroom, "The Celestial and Lunar Chamber."
Twilight sighed in contentment at the memories, but then she recalled their deaths.
Rainbow Dash's marred body. Applejack's strangled body. Rarity's body holding a knife and expression of helplessness. Pinkie Pie's blood, lifeless color, and frown.
More tears fell as she recalled the killer: and soft yellow pegasus with a luscious pink mane and tail.
Twilight refused to think of her name.
Finally, she felt her hooves brush the ground. She fluttered her wings, hovered, and landed daintily.
"I see you have arrived," a male voice announced.
A gray stallion with blood red, draconian eyes stared at her with interest and wisdom.
"I feared you wouldn't come," Sombra continued. He wasn't wearing any accessories.
"Sombra," Twilight said with a welcoming nod.
"Princess," he replied with a nod of his own. "Shall we get started, then?"
Twilight closed her eyes and took a deep breath, and she slowly released it.
She opened her eyes full of determination. "We shall."
Twilight was running with a panicked and fearful expression plastered on her face. She quickly whipped her head backwards. A loud, fierce roar bellowed. She looked forward and ran faster.
Sombra had cancelled out her magic that allowed her to fly with her non-proportional wings. He had also cancelled out her normal magic, leaving her, technically, as an earth pony.
The roar resounded again, but it sounded closer this time.
Suddenly, something inside Twilight exploded in rage.
"That's it," she whispered angrily. "I'm not running anymore..."
She turned towards the roar, and its creator appeared. It was a black ursa major with blood red eyes. Its sharp teeth were clearly unhygienic and dripped with blood and had meat between its teeth from previous... encounters.
Twilight narrowed her eyes at the beast. Then, a spark of purple, black, and sickly green sparked around her horn. Her eyes turned to midnight black with purple mist seeping from her them.
She screamed in rage at the beast as dark magic discharged from her horn and struck the beast with a loud snap.
The black faded from Twilight's eyes, revealing the mangled form of the Ursa Major. Blood was leaking from its chest at surprising speeds.
Suddenly, Sombra appeared with a large grin in front of Twilight. His horn bubbled with dark magic, and the black ursa major began disintegrating.
"Well done, Twilight," he praised. "You successfully killed something without any normal magic. I admit, I'm impressed. I didn't expect you to kill it so fast."
"Thank you, mentor," Twilight said with sickly green surrounding her irises and purple mist wafting from her eyes. "Shall we return to the castle, my King?"
Sombra's grin widened at the magic taking hold of his student.
"Of course, Twilight..."
Sombra was lying on a bed, relaxing while Twilight was cuddled up to left of him. She nuzzled his chest and breathed in the scent of his fur. She began wrapping her hooves around Sombra's waist, much to his pleasure.
He began moving his right hoof to Twilight's back, where he began to caress her plot. He slowly made his way down to her left leg. He grabbed it and proceeded to guide her leg to on top of his flank.
Twilight pressed herself against Sombra after finding this position easy to cuddle with him. As he felt her chest press against his, he moved his hoof back down to her plot. He craned his neck over her head and nibbled her left ear, and Twilight let out a moan of pleasure. In return, she gave a little lick to his chest.
Sombra smiled as his love's breaths became steady and easy. The smile twisted into a hideous smirk.
He released a chuckle as his magic created an obsidian knife.
"Twilight," he whispered, "I'm pleased to say you've passed the first test... And now, you get your reward..."
He jerked the knife into motion with his magic. He quickly brought it to her wing and began cutting the feathers, leaving a deformed wing that was bleeding everywhere.
Yet, Twilight did not wake. She simply continued sleeping with steady and easy breaths, all the while cuddling Sombra and pressing herself against him.
"Don't worry, my Queen," Sombra whispered. "It's for you. You will become perfect. You will become faithful. You will become broken."
He leaned over to her ear and gave another nibble.
"... You will become the dusk..."
Author's Note
Short, rushed, bla, bla, bla...
Cool story, bro... 
A large, dark cloaked figure galloped through the darkness, creating sound whenever she hit the ground. To think, after all those years of lessons, she had learned everything. This was her test.
She zipped along the streets with a buildings up against each other on the sides. All lights were off, and there was nopony out tonight.
She skidded to halt when she reached the end of the street. With the swift motion of a lavender hoof, the figure removed the hood of her cloak. She was a lavender unicorn with a long, unwell-kept, navy, purple, and pink mane. Her long horn protruded from her forlorn between her mane. Her right (your left) eye were a fierce and hurt purple with a touch of despair. Her squared muzzle had a pink scar right across her mouth. Another scar ran over her left eye (your right) where a sickly green energy wafted out of the scar on the eye, but not her skin.
She ripped off her cloak revealing large, lavender wings folded on her sides. Her tail was in the same condition as her mane. A large scar ran across her right wing, while showing tattered feathers as well.
Twilight Sparkle the Princess and Alicorn of Friendship and Magic.
She was currently performing her final test for her mentor. The task her mentor had given her was to kill a specific pony...
And Twilight Sparkle was eager to perform the deed.
How did she become like this: a murderer?
