Here's what I've got currently. I'm hoping to acquire original artwork at some point, but this is currently the best 'Fighting Adult Nyx' image I could find.

I know how important the short description is. If anyone thinks it needs improving, make your suggestions here.

Title:
Nitemare Nyx: Protector of Ponies

Short Description:
How can Nyx resist her darkest temptations while trying to overcome the greatest adversary of her life, all while the Great War against the zebras rages around her? Can she discover her virtue before all is lost?

Long Description:
The alicorn Nyx Sparkle, formerly Nightmare Moon, must confront her darkest temptations in the delicate balance between protecting the ponies she loves, and losing her own identity. Nyx and her friends face a brutal new threat to Equestria during the Great War against the zebras, and uncover the sinister ambition of a powerful adversary that threatens ponies and zebras alike.

Many thanks and all credit for Nyx and Fallout Equestria go to Pen Stroke and Kkat respectively. Thanks go to RealitiyCheck for Flitter.

Cover art by Sevireth

Prereader credit goes to:

Pawz, for general help with consistency and some pretty creative ideas.

onlyanorthernsong, for his excellent feedback helping to keep Nyx in-character and general writing advice.

Alcatraz, for proofreading and prose suggestions.

TundraStanza for meticulous grammar corrections.

Cover Art:

It's great so far. Are you set on the title?I'd sleep on it, I think it could to do be tweaked to the degree where it fits perfectly with the rest of the story, and I'm not 100% sold on it.

The alicorn Nyx Sparkle

I think that a comma could go after 'alicorn' It's just me, but it reads smoother.

Nyx and her friends face a brutal new threat to Equestria during the Great War against the zebras

This is the events before the great war, not during. Think Red Dawn. It's not a total invasion, that doesn't happen until about a year or so before the bombs drop.

Suggested rewording: "Nyx and her friends face a brutal new threat to Equestria during the events leading to the Great War against the zebras"

The period known as the Great War is officially the ~20 year span between when the Wonderbolts were killed rescuing captives from zebra pirates, and opening hostilities in the conflict over coal and gems - through the next twenty years until the megaspells were detonated. The mid-point of the war is considered when the Shit Hit The Fan, after the Littlehorn massacre. It was not long after that when things escalated into armored combat, with the Steel Rangers coming into play, as well as dragons fighting on the zebras' side. It's not long after the events of my story that Big Mac dies protecting Celestia from assassination shortly after the huge battle of Shattered Hoof Ridge. Before that even, we have the story of Steelhooves, who was saved by the first Megaspell field test. He was in a major battle as well. The war is definitely currently underway. The front lines are just not anywhere near Ponyville or Canterlot.

As for the title, that is actually the official name of the line of children's toys created by the Ministry of Image in my story, which depict Nyx as a badass combat hero. The toy line is meant to book-end the entire story. We saw the first reference already in Chapter 2, and the story will end in the aftermath of the big confrontation where Nyx discovers her virtue. The toys will be on the nightstands and in the play rooms of a great number of Equestrian children, as a reminder of who is watching over them. The toys are actually a foreshadowing - a representation of what Nyx will become over the course of this story. In the beginning, they depict her as mighty and fearless. A valiant hero, despite the fact that Nyx really isn't that yet in the beginning of the story. Not really. And yet, by the end of the book, she will become exactly what the toys depicted all along. That is why I chose the title.

while that is by far my favorite adult Nyx image as well, i believe it is used as well by the OTHER Fallout equestria/ past Sins story.

also I would give Credit to RealityCheck not only for Flitter but also Rumble, since he is the one who first paired him off with Nyx.

those are by far the most gracious and detailed thanks I have ever seen given out to prereaders/ editors before. I feel so very flattered! so very nice of you!