You might not know the context of this if you've not read the IDW comics... but this is the villain from the second story arc (issues 5-8)
The comics are really great, you should read them if you haven't!
Nightmare Rarity is really awesomely designed. It seems that EVIL makes her mane even MORE fabulous!
This was a lot of work, but i'm pleased with how it came out. Enjoy!