The Deal
Rainbow Dash tried to navigate her way through the maze in order to find the Elements of Harmony, only for her to encounter Discord, sitting in a cloud hammock. He seemed to be enjoying himself, as he sipped lemonade from a glass.
"What do you want?" she demanded of him angrily.
"Oh, relax, Rainbow Dash, I'm not here to hurt you," Discord replied, "I just want to deliver a message."
"Well, I've got a message for ya," she snarked as she raised her front hooves, "Meet my friends Arnold and Sylvester!" she added as she threw air punches with her left and right hooves, respectively.
"It's very important," Discord told her sternly, as he showed her a vision.
Cloudsdale was falling apart, as if by some sort of earthquake. Buildings were collapsing and ponies were panicking.
"This is what will happen if you don't do something about it," he told her, holding out a box. "This box contains your wings. If you want to go back to Cloudsdale, use them."
Rainbow Dash, dazed from her vision, shook her head and snapped out of it.
"No way," she said, "I'd rather die than be a part of your mind games."
"Suit yourself." Discord shrugged as he snapped his fingers.
Suddenly, Rainbow Dash's airways closed off. She died within seconds.
-----
Rainbow Dash woke up to find herself on a stone floor. She looked around and saw dark mountains among a red sky. It was very hot, and she saw there were pools of lava off in the distance. She could only assume it was Tartarus.
"Tartarus?" she asked herself, "But why?"
"In due time, little one," said a deep male voice behind her.
She turned around, and saw a large, dark grey male alicorn, with orange eyes, a mane and tail made of fire, and a cutie mark of a skull.
"Welcome, Rainbow Dash," he said, "I am Hades, Prince of the Dead and Keeper of Tartarus. Come with me."
Rainbow Dash got up and walked with him. "How... how has nopony heard of you?"
He sighed and said, "Because only those who come here and the Princesses know I exist. I make sure nothing escapes Tartarus, a prison realm built to house Equestria's most dangerous threats."
"Like Discord?" said Rainbow Dash curiously.
"Exactly," replied Hades, "And your decision to die as opposed to betraying Equestria and your friends due to his manipulation was most admirable."
"Well, yeah!" she said smugly, "I never leave my friends hangin', much less Equestria."
"However, Tartarus has a slight... problem," Hades said. "Security is starting to weaken. You see, Discord's soul was trapped here whilst he was imprisoned. When he was released, he left a crack in our realm through which prisoners can escape."
"What does this have to do with me?" Rainbow asked.
"I have brought you to Tartarus for a purpose. It is of great importance," he began, "I require a personal bounty hunter to return escaped souls to Tartarus. A 'Soul Hunter,' if you will. And I believe you are perfect for that task."
Rainbow Dash's eyes widened at this prospect. Help the Prince of the Dead recapture escaped prisoners?! That sounded awesome!
"That sounds badass," she replied.
"However, there is a price," Hades continued, "If you accept, you will be unrecognizeable to anypony who knew you before. You will no longer be able to live in regular society, either."
"And if I say no?"
"Then you'll remain dead, and your soul will be transported to limbo."
Rainbow Dash considered her dilemma carefully. One the one hoof, she could live again and be a bounty hunter for the Keeper of Tartarus, but she'd never see her friends again. On the other hoof, she could refuse, and her soul would be at peace, but she would also cease to exist. She had quite the decision to make. Then she remembered her death, and what she died for.
She had died to protect her friends, in an ultimate act of loyalty. She had chosen to die not just for herself, not just for her friends, not just for Cloudsdale, but for Equestria as a whole. If she refused, then she would have died for nothing. But if she accepted, she could do something to protect Equestria and make sure her death was avenged.
"I want to protect Equestria," she told him after much consideration. "I'll take you up on your offer."
Hades smiled. "Many thanks, Rainbow Dash. I am grateful for your help."
"So, what happens ne-" But before she could continue, she was lifted up into the air by an invisible force. Her fur, mane and tail began to catch fire, as her eyes glowed white. Her fur and hair had been replaced by fire. She was then set down as wings of fire sprouted out of her fur.
"Whoa," she said, in a substantially deeper voice. "Cool!"
"I'm glad you like your new form," Hades told her. "It will multiply your already incredible strength and speed by ten."
"Thank you, sir," Rainbow Dash said, bowing. "So who's my first target?"
"Your first target is Discord."
Rainbow Dash was shocked. How could she take on Discord so soon? She had no training!
"Sir, if I may, I need a little warm-up before I nab the big one," she requested.
"What kind of training do you require?" he asked her.
"I need to learn to hone my new abilities, and maybe learn a few tricks."
"Of course." Hades chuckled slightly. "You didn't expect to capture him immediately, did you?"
"Not really," she replied.
"Then let us begin."