Muffins (My Little Pony)

Muffins, also known as Derpy or Ditzy Doo, is a character from the My Little Pony: Friendship is Magic franchise.

Muffins is a Pegasus-pony and a good friend of Rainbow Dash. Her cutie mark is a set of 7 bubbles in various sizes.

Appearance
Muffin is a wall-eyed pegasus with a gray coat and yellow mane and eyes, and her cutie mark is a group of bubbles.

Personality
Derpy place her somewhere on the following four-point scale, one attempt at categorizing the different interpretations the character enjoys in fan labor:
 * 1: The diligent mail pony: She is a sweet and hard-working mare who everyone likes and depends on. She delivers the mail for Ponyville and is the very ideal of the reliable postal worker. Neither rain, nor Dragons nor Griffons will stop her from getting your mail to you. Her vision is impaired, but that's all that's unusual about her. Respected by all of Ponyville. This version was named by fans as "Bright Eyes."
 * 2: The day-dreamer: She is quite often out of it, lost in her own little world. Being easily distractable and blessed with a childlike attitude, her mind and attention are constantly shifting from place to place, but this often means she can notice things other ponies easily miss. Despite her aloof state of mind, she delivers the mail with utmost speed and efficiency. Other ponies see her as scatterbrained but dependable. Based on her scene in The Last Round-up, this is most likely where Derpy's canon personality sits.
 * 3: The Space Cadet: Her words and actions are totally nonsensical, and she seems to be completely insane. However, sometimes her statements make sense in retrospect or have an kind of odd logic behind them. This leads some ponies to believe that she is actually extremely intelligent, but she acts so strange that it is difficult to know for sure. Still delivers the mail flawlessly, to the surprise of many, though some ponies say this proves her hidden brilliance.
 * 4: The drooling idiot: Incapable of saying anything but "derp", "Muffins," and the like. Mentally challenged. Practically every concept more complex than “fire bad, tree pretty” is light years beyond her. She is genuinely happy, though, and capable of affection and kindness. Delivers the mail by accident. Walks into walls, often repeatedly, like a wind-up toy. Other ponies just try to make sure she's taken care of.

In the early days of the fandom, most portrayals of Derpy tended toward the two extremes of the spectrum. More recently, Derpy is more commonly portrayed around 2 or 3, with 4 becoming quite rare. This has become especially true since the introduction of Dinky Hooves.

According to an interview with former supervising director Jayson Thiessen (who had left the show to work on the 2017 film full time at the time it took place), the show-runners always viewed her as a "lovable klutz just trying to do her best".

Trivia

 * Her love of muffins and job as a mailmare are Ascended Fanon referenced in official merchandise, but weren't featured in the show prominently until the episode "Slice of Life". She's seen in mailmare uniform in "Crusaders of the Lost Mark", and delivers a letter to Starlight in "To Where and Back Again – Part 1".
 * Likewise, the name "Muffins" was only given in merchandise and the credits for "Slice of Life", and hasn't been said in the show yet.
 * She was just one of many other background ponies, but her ridiculous popularity catapulted her to recurring extra with a few speaking parts here and there. In a series somewhat infamous for the popularity of its background characters, Derpy is unquestionably the  most  popular.
 * An extremely downplayed example that only becomes evident by examining a Meaningful Background Event. In "Parental Glideance", there's a sequence showing Rainbow Dash taking part in flying competitions and moving higher and higher up the podium each time. Derpy is also present in the sequence: she starts at the  top  of the podium (even above other ponies who would go on to be Wonderbolts) and moves down a spot each competition, as her eyes become progressively more and more crossed, implying that she could've been a Wonderbolt-tier flyer if it weren't for her eyes. Adding to this is a brief shot of her at the hospital wearing a bandage over her eyes in "Where the Apple Lies", implying that she tried to have her eyes fixed, but it didn't work.