I always wondered why I felt a weird uncanniness toward Nightmare Rarity, but with this particular creation, I think I know what that is now: She reminds me of Queen Beryl from that old anime, Sailor Moon. She's even got the pointy tiara thingy! I guess it just took a proper humanization for it to finally click.
Anyway, all gushing aside, this looks pretty great. I don't think much more need be said.