Nightmare Moon returned after a thousand years of exile, and the princess of day and night vied for supremacy in the skies above Canterlot. For three days they fought, and all the ground shook with the echoes of their mighty clash. The sight of their battle was like thunder and lightning blasting through the sky, rocking the very foundations of the earth. But on the morning of the fourth day, Celestia proved the stronger. Nightmare Moon was driven from the sky and banished to the Northern Wastelands.
But something happened which Celestia did not foresee... The Crystal Empire has returned, and Emperor Sombra is prepared to do battle against Equestria once again. But this time, he has a new ally, the most brilliant general in all the world. This time he has Nightmare Moon.
And how do the Mane Six fit in on all of this?
"War changes, My Lady."
War never changes
War never changes, just the way we fight them...
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War never changes the same way water is not ice.
Well, this can't be the Crystal War timeline, really. Because in that one, Sombra uses mind-control helmets to force the Crystal Ponies into battle.
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They don't.
Welp, this one is going in the favorites! Yeah, this is totally something I'd reread. You've just gotta love the honor in the heart of Nightmare Moon. You did a great job keeping her and Sombra how they should be, though I do think Sombra's use of the word "idiots" is a bit too modern, and I think that "buffoons" would have been much more fitting. Also, you may want to seek an editor for this story. There are a lot of little mistakes: too many to point out. Here's one, though:
You want to use "than" here. "Then" is used to describe time. For example, I kissed Twilight, and then I hugged her tighter than a corset.
This is quite good. Though Sombra is definitely in disadvantage should NM turn on him once Celestial is dead.
Nightmare moon is Basically Erwin Rommel... And thats completely fine by me