Character: maud pie
Like Shining Armor, Maud is a relative of one of the Six who was introduced out of fucking nowhere and whose existence makes no sense given what we knew at the time about her sister. Unlike Shining Armor, nobody gives a rat's ass about that, because Maud is the stone cold shit. Maud first appeared in the appropriately titled Season Four episode Maud Pie in which she paid a visit to her sister Pinkie Pie and her friends.
Maud has the personality of a Norwegian on valium, meaning that she displays absolutely no outward emotions. She constantly wears a blank, half-lidded expression. She also wears a short and simple cobalt blue dress making her one of the rare few non-nudists in Equestria. Her mane and tail are solid purple, and her coat is stone-grey.
Despite her statue-like demeanor, Maud does have one all-consuming passion: rocks. She writes poetry about rocks. She talks endlessly about rocks. She uses rocks as kitchen appliances. She plays an intense variation of hide-and-seek called "camoflage" with her pet rock, "Boulder." Yes, she has a pet rock like it is still the Seventies, and it is just a common rock.
You may have figured out by now that Maud is likely completely insane. Thankfully, she does not seem to be dangerous, although she does inexplicably have super strength which she demonstrated by using the Fist of the North Star to pound a giant boulder into rubble in a matter of two seconds.
A curious quality of Maud is that she has a kind of drab fashion sense. Like Rarity, she wears eye shadow, and she has long eyelashes that she has trained into a thick wave. She enjoys accessorizing her outfit, but her choices include using a dirty dish towel as a scarf.
If you are wondering what it is that makes this complete fucking loon so awesome, the answer lies in how she reacts to the world and how the world in turn reacts to her. Maud has her own unique perspective on everything, seeing real world subjects and situations in the context of her own interests. That is a hallmark of well-conceived fictional characters. Her personality creates an awkward tension with everyone around her save for her sister. That makes for a comedy gold mine that produces exceptionally well in a show that
is was at its essense about personal interactions.
Best of all, there is some mystery to Maud that makes anything that she does something of a surprise. Since she never drops the poker face, we never get any clue to what she is thinking. When she uses a rock to "peel" (read "smash") an apple, for example, it makes perfect sense for the character but is otherwise unpredictable.