Derpy, also known as Muffins and Ditzy Doo, is a female Pegasus pony who was given the name Derpy Hooves by the show's internet following due to her cross-eyed "derpy" expression in the first episode. The name has since been adopted by the crew and Hasbro. Starting with Feeling Pinkie Keen, the show's crew began giving the pony crossed eyes intentionally and later gave her "Where's Waldo" type cameo appearances as a nod to the fans. The character is addressed by Rainbow Dash in The Last Roundup as Derpy, where she speaks for the first time. The scene was later altered so Rainbow no longer names Derpy, in addition to her voice being altered and eyes being less crossed. She is called Equestrian Mailmare or Bubbly Mare, among various others, in some merchandise. She shares her design with Sunshower Raindrops.

She's mostly a background character, mostly cameo appearances in the series until she was officially recognized by Faust herself. She's got something of a cult following despite having no spoken lines and her name was selected by the series' fandom's nickname for her. Though, in one of the episodes, there was said to be a clumsy pony by the name of "Ditzie Doo", and most of the fandom believe Ms. Faust did this on purpose. Usually, in any fan art of her, Derpy is reciting the famous line of "Muffins!", which was most likely rumored that she loves, because in the episode named "Applebuck Season", where Pinkie Pie and Applejack accidentally messed up a Muffin Recipe, she was in the crowd and there seemed to be a rather deep and wopsided-sounding "Muffins!" in the background.

Her first speaking role was in season 2 episode 14(40) where she was voiced by Tabitha St. Germain and she was officially named "Derpy" by Rainbow Dash. This scene however caused outrage and DHX took down the episode and had Tabitha St. Germain and Ashleigh Ball to redub their lines, removing the name Derpy and slightly un-derping Derpy's eyes.

Comparison of her old and new version

In season 5 episode 8 (100) Slice of Life Derpy was credited as "Muffin".