An interesting piece i must say, the colors are very well picked in this picture from the mix of background colors to the inverted, complimentary colors in the mane.
it's an interesting way to picture Nightmare Moon as the sad depressed type as she seems like the kind of arrogant or even 'full of herself' kind of attitude she tends to give off. Yet in this picture she seems more of the fragile type of person, as if Luna might pop out of her at any given time. It truly makes me rethink how I see Nightmare Moon herself.
You, as an artist have a interesting art style, instead of drawing out the rocks and adding texture it's as if you cut out, or etched out the background. It reminds me of when i was a kid how I would have those rainbow scratch cards that created a design as you scratched off the black.
all in all this is a wonderful piece of art and I loved it very much ^^ deffinitley somethign I will be sure to add to my favorites