Because it was requested, and I really like these costume designs, I've decided to post each of the ponies from my 'Halloween in Equestria' picture here separately, and full-size. Feel free to use them for whatever you want.
Twilight Sparkle as Princess Celestia. She's a total Celestia fangirl, it's silly. And I can't help but laugh at the fact that she has simple tie-on wings when she could just make some using magic.