Character: princess cadance
Originally conceived by Lauren Faust as a simple unicorn who used to babysit loli Twilight Sparkle, Cadence was completely redesigned before the Season Two finale aired, presumably at a party featuring great piles of cocaine. As she now appears, Cadence is an alicorn princess with the "Luna" body. She has a pink coat and super-long flowing, many-colored hair upon which she wears a princess tiara. Also, she is the ruler of the Crystal Empire that appeared out of fucking nowhere, much like her husband Shining Armor. She is the princess of love (scootaloogagging.jpg) and as such has the power to magically compel random peasants to fall in love.
Yes, Cadence (christened Mi Amore Cadenza...seriously) is a perfect, pretty, pink, pony princess who everybody loves and who married a handsome prince and who rules a magical happy kingdom--everthing to which Mom's FiM was antithetic. Despite appearing in two two-part episodes and two regular episodes, she has yet to manifest a personality. In that way, she really is the perfect match for Shining Armor.
Yet, it is difficult to truly hate Cadence for it. One reason for that is that she is tremendously long-suffering. Everytime she is on screen she is being tormented, threatened, tousseled, tossed, or otherwise treated terribly, and it all happens without a hint of sadistic self-awareness on the part of the show's creators. Cadence is Poor Pauline. It is difficult not to feel for her.
Another reason is that, despite being the animated embodiment of Mary Sue, she is never really the focus of the action. She is a peripheral character in her own story, overshadowed by powerful and interesting personalities like Twilight Sparkle, Rarity, and Discord. Cadence is there, but the story is never really about her, unlike other Mary Sues who never stop standing under the spotlight.
Finally, Cadence has one extraordinary quality that endears her to fans: she is great in porn. Fan "artists" find endlessly fertile fields in her to plow, as her lack of a distinct personality allows them to project her into just about any fantasy they can imagine. She even comes ready-made with a couple of fetishes courtesy of the show. Her design may be ridiculously overwrought, but it is appealing, so to speak, to horsefuckers in general.
Taken for all she is, Princess Cadence is a guilty pleasure.
In the Season Five episode The One Where Pinkie Knows, Cadence was revealed to be pregnant. Trailers for Season Six show what her newborn, named Flurry Heart will look like. The striped alicorn infant with comically large wings and a horn so long as to make any imagining of its birth seem horrific (add that to the list of traumas that Cadence has suffered) likely greatly pissed off any of the remaining fans who have thus far managed to cling desperately to the hope that the canon can be salvaged.