But in the description you said you dont know if it looks good Therefore I am trying to help you, It looks really cool but the cutie mark draws attention from Nightmare Moon herself, plus her cutie mark isnt the prettiest because its just a blob unlike twilights, you dont need to be rude.
I think you honestly did the best that could possibly be done. I've never been a fan of how Nightmare Moon's mane looks, as if it isn't really attached to her head. So she kinda looks bald to me, but you made this look as good as it could possibly look.
I agree, this one is questionable. Although that might be just because I am not a great fan of Nightmare Moon. I guess if I look at it art-wise, it is pretty good. The moon and the clouds in the background look pretty awesome.