I wanted a subtle MLP:FiM wallpaper for my computer, and seeing Nightmare Moon (and Luna) is one of my favorite characters on the show, I wanted it to be of her. However, I couldn't find any NMM cutie mark wallpapers, I decided to make my own.
Size is 1366x768. If people want a larger version I can make one.
MLP:FiM (C) Hasbro
You are free to use this wallpaper for your desktop if you want.