DISCLAIMER: Ms Rowling owns all rights to Mundungus Fletcher. I doubt no one else would ever claim him.
Chapter 1 - By the River Styx
Mundungus Fletcher cautiously opened his left eye and identified the substance under his left cheek as a dull, black sand he'd never seen before. He opened his right eye and confirmed that it was sand. Dull, black sand, as far as he could see. And as for noises, well, there wasn't too much sound, really. Just the lapping of water on the sand behind him.
Mundungus sat up and looked behind him. Yes, there was water there. And it was bubbling with fire, little jets that popped up here and there, perhaps a form of swamp gas, he mused. He couldn't see very far over the water, though, there was some sort of fog. And something was coming through it, over the water. He clambered to his feet and tried to focus on it.
Through the fog came a boat which was punted by a morose and grisly old man in a black sailor's cape. The man beached the boat, looked up at Mundungus, and said in a gravelly voice, "OK, Fletcher, where's the coin?"
Mundungus, who had never studied classical literature and had no idea who this man was, opened his mouth to reply, "What coin?" and was shocked to discover a sickle falling from his mouth. He caught it and held it up to the man. Charon plucked the coin from the startled wizard's hand and said, "Come on, Fletcher, get in the boat."
As Mundungus got in, he realized that he had no control over his body. It was as if he were under an Imperius curse, yet he was perfectly aware of his surroundings and didn't have a nagging little voice in his head telling him what to do. This was more like being a puppet, and he didn't like it. He tried to ask the man who he was and where they were going, but his mouth stayed shut. And so, he was totally shocked when the man answered him.
"I am Charon, the ferryman of the dead. That's right, Fletcher, you're dead. As dead as anyone would be who'd run afoul of Lucius Malfoy while breaking into Malfoy Manor. That coin was placed in your mouth by a friend of yours at your funeral."
Mundungus tried to remember ever being at Malfoy Manor, but he couldn't. The last thing he remembered was sitting at the Hogshead, trying to overhear a conversation Hagrid was having with a heavily cloaked stranger. After that, it was all a blur.
"Well, here we are," said Charon as the boat ground into the sand on the other bank of the river. "Just go on into the cavern behind Cerebus, and don't try to come back out. He'd enjoy munching on you."
Mundungus watched himself jump onto the shore and walk calmly past a huge, three-headed dog which was snoring quietly. He found himself wondering if Hagrid knew about it. It looked like the sort of dog Hagrid would love. Suddenly he found himself in control of his body again. He took a step back toward the dog, then whipped around and fled it as it sprang to its feet and all three heads snapped at him!
He skidded to a halt before a tall, dark man dressed in a blue robe. "Welcome to my realm, Mundungus Fletcher. I am Lord Hades."
"Who?" blurted Mundungus. "I thought Hades was just another name for, well, Hell."
"My realm bears my name, Fletcher. I am the god of the Underworld, and my realm contains many lands. I send the heroic, good people to everlasting joy in the Elysian Fields. You aren't going there."
"What?" gasped Mundungus, who knew he was anything but heroic and not a particularly good man, but he had hoped for everlasting joy should there be an afterlife.
"No, you abundantly qualified yourself for Tantalus, the part of my realm that most people mean when they talk about Hell. In fact, thanks to you, not too many people will ever again go to the happier lands."
"Wha-- you mean I've done somethin' to mess things up agin?" asked poor, confused Mundungus.
"Oh, yes," replied the god. "You messed things up beyond belief. You made it impossible for anyone to ever overcome Lord Voldemort."
Mundungus stared at the god, his mouth opening and closing, but no words would come. Finally, Hades answered the question Mundungus couldn't bear to ask.
"Do you remember stealing a heavy, gold locket from Number 12 Grimmauld Place? A locket no one could open? A locket you sold in Borgin and Burkes?"
Mundungus nodded helplessly.
"That locket was a key part of the puzzle that Harry Potter had to solve in order to defeat Voldemort. Thanks to you, it ended up again in the hands of Voldemort, who found a safer place for it. Thanks to you, Potter was unable to return Voldemort to his mortal state and kill him."
Mundungus fell to his knees and covered his face with his hands.
Hades continued, "Thanks to you, Voldemort will never die. He will conquer both the Wizarding and Muggle worlds. He will rule over the entire world to the end of time.
"And so, Mundungus Fletcher, you have certainly earned an eternity in Tantalus."
Two demons appeared on either side of Mundungus, grabbed him by his arms, and dragged him away into the darkness.
The End