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.
Pinkie Pie as Gummy (and Gummy as Pinkie Pie). These two are a little bizarre, but then, it IS Pinkie Pie. And it looks like she's all set to go trick-or-treating.