Well, the portrait is one that depicts villains and Derpy isn't a villain. Not that I have a problem with the image because I don't, I just didn't get why she was in the image when the point behind the portrait was to get Discord, Queen Chrysalis and Nightmare Moon together in the image. I didn't mean any offense because who doesn't like Derpy? She's a muffin crazed disaster who's hilarious.
Heh, The mane three antagonists. Nopony would want to mess with any of them in a dark alley. Truth be told, I have an idea for one that isn't as "merciful" as these guys. You can learn more about him in my upcoming fan-fic: MLP:AIP. (Intro chapter's already up if you want to check it out)