Talk:Episodes, films, and shorts/@comment-27515470-20150428112910/@comment-4531340-20150428204040

Basically, my understanding of the Derpy thing is that one of the artists made her eyes derped in the first episode as a joke, because her face was originally hidden behind another pony but a layout change revealed her. She was named Derpy Hooves by someone on 4chan's /co/ board, and gained enough popularity that Jayson Thiessen had her eyes derped in all episodes not yet sent to the Hub (apparently, Feeling Pinkie Keen forward). It was also about this time, I think (I wasn't a brony yet so I don't really know) that the crew announced that the two background pony names they had adopted for usage by them (but obviously not by Hasbro or anything released to the public) were Derpy Hooves and Dr. Whooves.

Then, before season two, it was announced that Derpy would be a scripted character, specifically called for in the script, rather than appearing in the layout stage in order to fill a scene. Then there was her speaking role, and I think you know the rest.

I also like the idea that she's the fandom's unofficial mascot.