(Information on her partner, Akishme, can be found here. I hope to gain approval for writing them as my Agents.)
Penchant is a unicorn pony recruited from a My Little Pony badfic. She was described as being "a dick, not understanding Twilight's love for him!" because she would often, rather harshly, tell the Sue-Twilight that she couldn't date Shining Armor, and make snarky comments (apparently the author didn't see how amusing said comments were). She was also created to be Twilight Sparkle's sister, and they "have the same colors but our manes are a bit different". Penchant isn't exactly happy about her origins or resembling a canon character, so she doesn't really talk about it.
Personality-wise, Penchant is a natural introvert. She's not unfriendly, per se; she's just socially gimped. She tries, though, really. Part of it is that, if asked for her opinion, she will give it exactly how she sees it. Penchant is brutally honest with people, as she feels sugar-coating things doesn't help. Even if she turns out to be right most of the time, it doesn't get her many friends. She gets easily annoyed with people, which also doesn't help. She's a no-nonsense kind of gal, and doesn't have a very high tolerance level. When annoyed, she snaps at people and, if they persist (and she happens to be knitting), she will jab them with her knitting needles. She doesn't really see a problem with her actions.
Knitting, reading, writing, and research are a few of the things Penchant actually enjoys. She doesn't like to be bothered when she's in the middle of something, and her already-low tolerance levels become non-existent. Penchant likes things to be calm and quiet, and will get upset if disrupted. Often times, she will recluse to her desk, surrounded by tall bookcases. The area makes her feel protected and she enjoys the solitude. She also enjoys insect collecting, and studying, taking care of, and breeding strange creatures. She has a particular interest in giant spiders and things with slime or spikes or tentacles.
In terms of interactions with her partner, as long as she can have alone time, Penchant gets along with Akishme just fine. The Argonian is able to get Penchant to loosen up and have fun, which is a pretty big accomplishment. They play games, crack jokes, and enjoy hanging out, however Penchant will become uncomfortable if Akishme already has company and invites her to join them, or vise versa. When it's just them, they have a lot of fun, though Akishme is skeptical of Penchant's love for... unusual creatures, and Penchant is wary of Akishme's harebrained schemes (she will go along with them, most of the time, but she's never too happy). They both think very highly of each other, and enjoy being partners. Something Penchant will never admit to is her envy of Akishme's ability to just talk to people and make friends.
Penchant is 5"8, with purple eyes, pale skin, and Twilight Sparkle-esque hair (dark blue, with a streak of both pink and purple). She's got a thin, lanky build, and small chest. Penchant isn't too fond of the way she looks, but prefers a human form a) because, after her experience with being in a badfic, she doesn't much identify as a pony, and despises looking very similar to a canon character, and b) she feels people won't really take her seriously as a candy-colored equine. As a pony, well, she looks very similar to Twilight Sparkle, but is missing a cutie mark.