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// Your Precious Moon 
// Story: Book 1 - The Behemoth came to Canterlot 
// by Equimorto 
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There was something ironic about the whole thing. Something deeply, maybe even beautifully ironic about it. The first time Twilight had properly experienced teleportation had been while being dragged into Nightmare Moon's own, all those years ago, in the ruins of the old castle. Not only was she returning the favour, she was also, while carrying Celestia's powers, doing what her former teacher had done to her sister, but to a version of her who had not experienced anything of the sort. If she'd had the time to, Twilight would have laughed. Of course, she didn't. There wouldn't have been much air to carry her laughter in, anyway.
Both mares appeared in a burst of golden light. Both were sent tumbling back from it, raising clouds of white dust that lingered airborne in the lower gravity of their new environment. Both alicorns stood again, looking at each other. Twilight almost winced feeling her weight over her legs, she only didn't fall over because she didn't have to bear as much of it as usual. Immediately she spread her wings and took off, raising another cloud of dust, shooting higher than she'd have expected.
Nightmare Moon's eyes followed her, and her maws opened in a mute growl as she lit her horn to strike once more. Twilight was prepared. She'd prepared for days. Her horn too began to glow, and sometime else did the same in response. A glyph, a rune carved into the lunar surface below them, not too far from Nightmare Moon's hooves. One of many, many others like it Twilight had carved on her last visit there, and only the first to be activated.
Before Nightmare Moon could strike, a harpoon of solid white light erupted from the rune and shot towards her, tied to a thick and heavy chain that sprouted alongside it from the ground. It bore through her body and seared her flesh, and her mouth burst open in a silent scream, tearing through the length of her neck to reveal rows of sharp, monstrous fangs.
Twilight didn't stop. Higher she rose into the Moon's black sky, setting off rune after rune as her horn shone brighter and brighter, each firing off towards her enemy as the first one had. Twilight with her protective spells had no need for air, no environmental hazards to worry about, and she kept soaring higher, high into space, enough to see the curvature of the Moon from where she was.
Something was happening to Nightmare Moon. Something had begun happening to her all the way back on Earth, and it was continuing to happen. Her body grew back with each wound she received, but it did not stop growing there, it did not rebuild what had been before. After merely a few shots sustained, she was far beyond looking anything like a pony.
An abomination spread its limbs and tentacles over the surface of the Moon, black as space without stars or light, only held down by the dozens, hundreds of chains that anchored it to the ground at Twilight's command. It screamed from toothed pits filled with eyes and watched from fang-covered mouths and writhed and spasmed as it poured ichor and death all around itself. Uncountable heads and faces rose and fell from its form, and new eyes grew over its shapeless body and new maws spread over it to cut through them and drink in its own blood.
It roared enough to shake the Moon itself, and Twilight felt it like a wave, not mere sound but magic and emotion and intent, blind rage and lust for destruction pouring skywards like a torrent as towers of molten, blackened flesh and teeth arose to reach her, too many for even the thousands of glyphs she controlled to stop them all.
That was all accounted for. Not the specifics, of course, but merely trapping Nightmare Moon on her namesake had always been just half of her plan. It was time for the hard part, and Twilight would see it through until it ended, or until it ended her.
Her horn shone brighter still, brighter than it had during the entire length of the battle that day. Part of her magic became a shield around her, a thin bubble of gold meant not to physically stop Nightmare Moon's tentacles to reach her, but to burn them if they did. Twilight closed her eyes, and she fell upwards away from the Moon.
The rest of her magic went to the glyphs. All of them, thousands of them all around the surface of the Moon, all at even intervals over its entire geography. They shone, bright as her horn, almost visible even beneath what had become of Nightmare Moon. Their chains shone with them. So did something else. Something far, far away, an infinite distance away, a world apart and yet there, exactly there, exactly in the same location. Twilight had only tested a spell like that once, on a much smaller scale.
The Moon, the glyphs, their chains, the creature tied to them, everything vibrated like the air above a fire. Everything went a little greyer, a little less there. Everything seemed to fade for a moment, before snapping back in. Twilight felt it, all of it, more than she felt herself at that point. She let go, of everything but the spell she was pouring herself into.
Her shield dissipated. Her limbs fell limp, unneeded to keep her flying as she surpassed the Moon's gravitational reach. Magic coursed through her entire body, shining brighter every moment, a miniature star between the planet and its satellite. Not just her horn. Her eyes snapped open as pure white flowed out of them, her mouth agape in a scream of light, her body impossible to see as the glow of her magic encompassed it whole.
Patches of the lunar surface seemed to explode, wiping away the abomination over them, encircled by a spreading edge of light. Something else entirely was happening. Portions of the creature's body were similarly engulfed, removed, taken far away and yet in the same place they'd been. The entirety of what was there trembled again, waned again, shivered and faded, and it did not stop.
The light around Twilight collapsed, then spread out like a sun exploding. In a single instant, a single last moment, every glyph on the Moon shone blindingly white, every chain sung with searing hot energy. Then it all was gone. A blink, and the Moon was all that was left, the light gone from it and from Twilight, the abomination gone alongside it.
In a stray bout on not yet unconsciousness, Twilight looked at her world's new Moon, once Nightmare Moon's. Then, the princess fell back to Earth.