Disclaimer: Harry Potter and friends belong to J.K Rowling, not me.
Down and down Draco fell into the abyss, screaming all the way. Finally he crashed unto the ground, feeling no pain as he no longer had a physical body. He opened his grey eyes and looked around. He was in a very red, very hot place that stank of sulphur and other vile odours. He was standing on a ledge overlooking a giant lake filled with a foul mixture of blood, feces, vomit and urine. Draco could make out people swimming in this putrid pool, screaming while winged demons flew overhead and jabbed at them with pitchforks. Draco beheld all this and was dismayed.
"Oh no! How did I get here? Wait, now I remember! Potter and his Mudblood friend Granger killed me! Damn it!"
Suddenly a tall, handsome man with a black goatee, thick horns growing out of his head and wearing a stylish black suit approached Draco.
"Ahhhhhhhh yes, Draco Malfoy. We've been expecting you. I am Satan, Prince of Hell and you have been condemned to my realm for your life of sin and blasphemy." Draco fell to his knees in shock.
"Nooooooooooooooooooo!" (A/N: Think Darth Vader in Revenge of the Sith!) he moaned in remorse. The Devil smiled.
"But I have a proposition for you. I detect within you the potential to become a powerful wizard. Become my apprentice, Draco, and I will teach all the forbidden magics Hogwarts would never dare to. I will send you forth back to the world of the living to carry out my bidding. You will become my right arm, my weapon, my servant. What do you say, Draco? Do you accept?" Draco considered Satan's offer. The Devil seemed honest enough , and it wasn't like he had anything to lose.
"When do we begin?" Draco asked. Satan smiled and laughed.
"Ah, enthusiasm- I like that! Come right this way…"
&&&&&&
Thus did Draco begin his training under Satan's tutelage. The fallen angel began instructing his protégé in the use of the blackest of the black magics. Draco proved to be an adept student, mastering Satan's lessons with ease, and his power subsequently began growing, and he was soon more powerful than he had ever been alive. The Devil was quite pleased and silently congratulating himself on choosing Draco as his apprentice. He had always been jealous of God and his son Jesus Christ, and had long wanted someone to play the son role in his life- someone he had now found in Draco.
One day, Satan summoned Draco before him. The ex-Hogwarts student kneeled before the Devil's throne, a grisly seat crafted from the skeletons of aborted babies.
"Draco Malfoy, I have a mission for you. It is time for you to return to the world above."
"Yes, my master."
"I hereby order you to kill Dumbledore. He is a powerful agent for the forces of good and one of God's Saints on earth. His existence is odious unto me and I demand you put an end to it." Draco nodded and stood up to leave. Just as he was about to reach the door to the throne, he heard the voice of his master behind him. "One more thing, Draco. You might encounter Harry Potter on your mission. He is not to be harmed! It is not yet his time to die." Draco grit his teeth and fought down the urge to protest.
"Very well." And he was gone.
&&&&&
Draco apparated near the castle and snuck onto the grounds. It should be noted that Draco's appearance had been changed by his time in Hell. His eyes were now bright red and glowed in the dark, and he now sported a pair of vampire-like fangs.
He approached the main entrance door and gave it a mighty kick. The massive oak doors splintered before his blow and he entered. Everywhere students of every age screamed and fled when they saw him coming. Draco marched slowly, as if daring someone to challenge him. Finally he reached the Gargoyle statue that marked the entrance to Dumbledore's office when he heard a voice behind him.
"Draco?"
He turned. Standing there was his nemesis, Harry Potter, his mouth agape in shock.
"But it's not possible. Hermione and I-"
"Killed me? Yes, you and the Mudblood did a good job of that."
"But how…?"
"Let's just say I serve a new master now. He took me in and…well, what can I say? I'm back!"
"A new master? Voldemort?"
"No. One far older and stronger. Tom Riddle is but a vengeful schoolboy compared to him."
"Wait, you don't mean-?" Harry went for his wand.
"Expelliarmus!" Draco shouted, having noticed Harry's motion a split-second earlier. Harry's wand flew away. Draco walked up to him.
"You're lucky I've been ordered to spare you. We'll have to leave our conclusion for another time." Draco's hand shot out and slapped Harry across the face. His rival fell to the floor, unconscious. He now turned to the Gargoyle.
"Fizzy Bubblemint," he said, using his new demonic powers to divine the password. He entered.
Inside, Dumbledore was writing on a piece of parchment. He did not look up when Draco came in.
"Mr. Malfoy, have a seat."
"Don't mind if I do." He sat and crossed his legs.
"Lemon drop?"
"Yes, thank you." Draco took a candy from the dish on the Headmaster's desk and popped it into his mouth.
No one said anything for several minutes. Finally Draco spoke.
"Aren't you curious as to why I've come back to life."
"No, as it isn't news to me. I've known about what's become of you since you accepted Lucifer's offer."
"Then I imagine you know he's sent me here to kill you."
"Correct."
Another period of silence.
"Isn't there anything you want to say or ask me?" Asked Draco, slightly exasperated with Dumbledore's nonchalentness.
"Only that I consider it a personal failing of mine that you accepted the Prince of Lies' offer. It shows that I failed to teach you the difference of right and wrong during your studies here."
Draco felt like he'd been hit. How dare Dumbledore try to discredit his apprenticeship on moral grounds! He jumped out of his chair and zapped Dumbledore's desk, causing it to explode. Dumbledore jumped out of the way in time.
So began their duel. Draco's expectations of a quick and easy victory were quickly broken. His former Headmaster was a formidable opponent. His hexes were as powerful and as they were numerous. Again and again Draco attacked with the forbidden magics he learned to little effect, as Dumbledore countered or blocked everything Draco threw at him.
Draco crashed against the wall and crumpled to the floor. He was exhausted. His face was cut, singed and bruised in various places from Dumbledore's magic. He was beaten. All that was left was for Dumbledore to finish him.
"How, damnit?" Draco wheezed.
"Your mistake, Mr. Malfoy, was believing that the spells taught to you by Hell had no equal. I simply countered using their elemental opposite magic."
"Divine magic," Draco muttered. "Damn you."
"Ironic given that I am not the one about to return to the Netherworld." Draco snarled and apparated back to Hell.
&&&&&
"So you've failed me," said Satan. His tone was not angry, merely disappointed.
"Again, I apologize," Said Draco, again kneeled before his Master's throne.
"I would be lying if said I wasn't deeply offended by your incompetence. For now I will pretend to forget this failing on your part in the hopes you will someday correct your mistake."
"Thank you, my Lord."
"I have another mission for you. Lord Voldemort has long been an irritation unto me. There is room for only one Dark Lord and that is me. Destroy him."
"I shall not fail."
"Not yet, however. It has become apparent that your training to date has been inadequate. You will prepare yourself further. Now get out of my sight."
"Yes, Master."