HP v Superman: Dawn of Justice
A man stood on the moon; specifically, the dark side of the moon. Though the man he looked only 20, he was actually 35 and known as a master of magic; though less known, was the fact that he was also a master of death. Magic cloaked him in a protecting shroud, a warming charm kept away the cold of space, and a bubblehead charm provided him air. A wand in his hand produced a soft light, a cloak on his shoulders shimmered in the light, and a ring on his hand drank that light in. As a child he was a soldier, obeying orders and killing what conventional logic said could not be killed. As a man he was a wanderer; going from place to place trying to help where he could, muggle or wizard, his aid knew no distinction. The man was here testing a new weapon.
Muggle science had advanced far within his lifetime, though for most of his life, he was ignorant of such science. Funnily enough it was only after he graduated school that he actually started learning the laws of nature that he regularly broke in his school days. And it was among the muggles, not the wizards, that he found the true power and potential of magic. For with magic you could create something from nothing, change one thing to another with no energy loss, grow and shrink things, remove things altogether from existence, or even rip wormholes into the fabric of space/time to fetch your groceries. Essentially, the law of conservation of mass meant nothing to wizards, and none of them knew what that meant except him. He was dearly hoping to keep it that way; after all, such knowledge helped him easily think of the weapon.
Transfiguration was a relatively simple discipline. Focus on an object, think on what you want it to change to, and will your magic to change it. Simple and requiring very little energy overall, the only real cost is in the amount of concentration required to effect the change. It was why magical battle masters often preferred large transfigurations in more heated battles. Big effect little price. Charms worked on similar principles, though in a passive fashion, longevity in effect with subtle manipulations upon the world gave far more than you put into it. His weapon was the optimization of this principle and it was why he was on the moon, as far away from humanity as possible. He had . . . concerns about the power output of his idea.
Really, the reason he was testing his theory in the first place was because the supernatural had been recently revealed to the world. Nothing magical, but Alien, with a capital A. Ships came to the planet and the whole event ended with super-powered beings brawling out their differences all over the destruction of the city of Metropolis. The victor of this fight, this Superman, claimed he was defending the world from being terraformed, that he was here in peace, and that he only wanted to help. Now, that was all well and good, but the problem was that should that not entirely be the truth, there was nothing the muggles could do about him either way. The green-eyed man had once had his own dealings with a ravenous public and media accusations and thus sympathized with Superman somewhat but the fact remained, what if Superman turned out to be dark? So here the man was, testing his idea for a new weapon - just in case.
The dark-haired man set about charming a series of magnetic fields looping above him in a circular track. He then levitated a pebble about the size of a fingernail, sealed it in a magical vacuum and transfigured it into the material he wanted. Cautiously, he floated the glowing material into the invisible magical and magnetic railway above him. As expected, his "pebble" started to accelerate quickly and blur on its track until it seemed as if an enormous halo made of a solid white bar floated above him. The man steeled himself, floated off the lunar surface, aimed at a miles distant crater . . . and launched his projectile. The resulting explosion was impressive, and the apparent damage even more so, but that was to be expected from an anti-matter rail gun. Still, the man frowned, the weapon needed work. It took too much time to deploy, and had only a single shot, but it was a start.
As the man casually ripped a hole in space-time in what he called apparition, he had a thought. "The weapon may not be ready for use yet, but it will be soon, and if Superman ever turns out to be dark. . . Well, I'm Harry Potter, and I can kill anything - even if it calls itself a God."
One-shot first try at a fanfic. Feel free to use any of my ideas if you want.