Hair-Trigger Temper: As in canon, but unlike in canon it's treated a genuine disorder. He's so mired in free-floating aggression and self-hate that he can't function, directing his rage either outward (and getting into fights he can't win) or inward (where it tears him up and flattens his self-esteem).
Hates Being Touched: As Gamzee discovered, to the dismay of both. One story demonstrates that Karkat doesn't much like seeing others touched against their will, either.
Jerk with a Heart of Gold: He may be blunt, tactless, abrasive, vocally opposed to social interaction and have a nitro-glycerine temper, but beneath all the yelling he's a deeply compassionate guy, tuned in with the emotional states of people he cares for, wanting to see them happy, and tragically convinced his presence just gets in the way.
Mixed Ancestry: His mom is from India and came to the US when she was a kid, while he refers to his dad as "a redneck", implying that he's bi-racial.
Mommy Issues: Probably only rivaled by Rose's. A good deal of Karkat's identity and temperament issues can be traced back to his emotionally abusive relationship with his mother (for starters, it's hinted that he smothers all emotions save incandescent rage because otherwise his feelings would be used as proof that he's "something [he's] not"). Eventually his mother seems to make efforts towards getting her own temper under control, which only mires Karkat deeper in self-loathing for not being able to improve himself accordingly.
Transsexual: He's a trans guy. There are very few patients who know, such as Dave, who was assigned to room with him precisely because the staff knew he wouldn't give a fuck; Jade, who is the glad recipient of all the girly clothes Karkat gets, and possibly Rose and Vriska.
Berserk Button: Lots of things can set Sollux off when he's on a downswing, but he goes nuclear whenever someone brings up Aradia to him in any way that could be construed as negative, as Karkat found out the hard way.
Freak Out: When Karkat pointed out, with his usual tact and civility, how Sollux's relationship with Aradia came off as dangerously codependent, Sollux bloodied Karkat's nose and tried to bodyslam through the nearest (locked) window before being sedated.
Geek Physiques: He's a computer genius, and quite thin. His bipolar disorder making him forget to eat when manic probably helps in this regard.
Platonic Life Partners: With Aradia. It wasn't always platonic, but they mutually agreed that it wasn't working out.
Shameless Fanservice Guy: Downplayed; in the early installments at least, he was prone to going around the hospital in a hospital gown, boxers and not much else. He didn't seem to care much until Clubs pointed it out to him.
Skinny Dipping: YAHOOOOOOOOOOOOOO! She is unaware cannon-balling into a stream minus clothes tends to surprise others somewhat. And may be illegal in Minnesota.
Beware the Nice Ones: Generally extremely affable. But when he returned Karkat's opening punch, he knocked the kid flat and left a black eye that didn't fade for two weeks. Something prompted learning to hit like that.
Cluster F-Bomb: In a completely non-hostile way. It's more like a Verbal Tic than anything else. Equius does not approve, however.
Gentle Giant: Described as such at one point. He's incredibly tall but about as malicious as a fluffy pillow.
In the Blood: The story told from the point of view of his father, Ches, implies that some of Gamzee's issues are hereditary.
Innocently Insensitive: Once in a while. He's a total sweetheart, but doesn't always think before he acts or talks. This mostly comes out in his dealings with Karkat and Sollux, both of whom have more than their fair share of Berserk Buttons that he has an unfortunate habit of unintentionally hitting.
Harmful to Minors: When he was a kid he witnessed his father attack his mother after he found out she was seeing someone elsenote his father had been in prison and only recently reconnected with them, and while he accepted his mother's polyamorous lifestyle, at least on the surface, he blew up when he thought she was deliberately keeping things from him, and it's implied he repressed this memory.
Stepford Smiler: Gamzee's spacey teddy-bear persona sometimes hangs on by a thread. He once had a particularly bad morning and spent most of the day in the Troubled Fetal Position, weeping his eyes out.
Supreme Chef: Provided he can be prevented from adding certain prohibited substances...although apparently, he can cook pretty spectacular things that include them as ingredients. He's just not allowed.
Wholesome Crossdresser: In his mermaid Halloween costume. He mentions that he enjoys modeling for Kanaya, which suggests that he doesn't pay much attention to gender conventions when he gets a chance to dress up.
According to Kanaya, he "Has Excellent Taste in Womens Clothes And Terrible Taste In Mens"
Base Breaker: She's not a lot less controversial in this Alternate Universe than she is in Homestuck proper, and since it's a fanfic, people who don't like her portrayal can complain that she's being written wrong. VastDerp has complained about the resulting deluge of fan opinions in his inbox.
Never My Fault: A lot, just like in canon. A notable example is when she mocks Calliope for having severe burns on her face, prompting John, Dave and even Karkat to get angry at her. Her response? It can easily be summed up as "It's just a joke! Jeez, would you lighten up?" Another unfortunate conviction of hers is that when she does bad things, gets reprimanded, and apologises, the situation is then immediately fine again - the injured party has no reason to feel any animosity or wariness toward her and if they do, they're just being unfair. After all, she said sorry!
Abusive Guardian: His brother, to put it mildly, is not fit to be a parent. A lot of Dave's problems stem from his refusal to admit this.
Celibate Hero/Asexuality: He's willing to talk (and joke) about sex and related issues in the abstract, but has yet to show any physical or romantic interest in any of the other characters, and he does not find the idea of having sex with anyone at all appealing.
Elective Mute: Goes "on strike" whenever he's under extreme stress and refuses to speak or interact with anyone, except occasionally Terezi and Nepeta.
Foregone Conclusion: Bro loses the hearing. Everyone knew it was coming except for Dave, who refused to consider the possibility.
Heroic Albino: Played straight and also deconstructed by showcasing the problems that real life albinos have because of their condition. Nystagmus (involuntary eye movement) and extreme sensitivity to light are among the worst of it.
Hidden Depths: He's also far more observant than some people realize. For instance, he already knows that Karkat is trans but doesn't feel it's worth commenting on, and Word of God is that they specifically placed them together because they knew he wouldn't care.
Missing Time: Something he frequently experiences. On on occasion he accidentally cut his hand open while home alone and then lost time, meaning he could have bled to death and not known it.
Self Harm: Puts cigarettes out on his arm. Usually doesn't seem completely aware he's doing it.
Asperger's Syndrome: A fairly accurate portrayal, all things considered - she's more eccentric and socially awkward than anything, and it's considered a non-issue by the staff as long as it doesn't affect her day-to-day functioning.
Brown Note: Because of her sensory processing issues, she can have very strong negative reactions to mundane stimuli. She has a particular loathing for purple.
And whatever perfume Kanaya was wearing that day. Holy shit.
Cat Girl: With her outfit and persona. Biologically, she's completely human.
Cat Smile: She has a slight cleft lip in some of the art that gives this effect.
Broken Ace: She was at least on the verge of becoming one - rich, intelligent, and accomplished, but full of hidden insecurities, parental ambivalence, and substance abuse issues. Unusually for the trope, she's actually getting help.
Beware the Quiet Ones: In his backstory, he got fed up with being bullied, and then decided to strike back, so he went to school dressed as his LARP character and broke the jaw of the first guy to give him shit about it.
The Dandy: A bit. At least, he is unusually style-conscious for a teenage boy.
Drama Queen: Apparently, when a cold epidemic swept through St. Lobaf's, he spent all of his time lying in bed with his hands folded over his chest funeral-style because he was convinced he was going to die. From a cold.
Giftedly Bad: As a writer of amateur fantasy fiction. Gamzee seems to like his work, but Gamzee seems to like everything. Eridan does have potential - it takes genuine talent to write prose that purple - but he's in dire need of constructive criticism and the confiscation of his thesaurus.
Straw Vegetarian: Atypical dietary habits/needs aren't uncommon at St. Lobaf's (for instance, Nepeta is very particular about the arrangement of her food due to her sensitivity to textures; Equius and WV are entirely pleasant vegetarians; and Gamzee has strong feelings about varieties of dessert). Really, nobody would have a problem with Eridan going vegan...if he didn't walk around trying to cram his moral superiority for doing so down everyone's throats.
Insistent Terminology: Eridan would like you to know that he owns an actual fedora, as opposed to those 'modern reimaginations a the fuckin trilby'.
Likes Older Women: He has a crush on Feferi, who in this universe is in her early thirties.
Lonely Rich Kid: His parents are pretty well-off, which fuelled a lot of the bullying he endured in school.
Megane: Unlike his canonical counterpart (who eventually fell into Four Eyes, Zero Soul territory), Eridan here is a shy, dorky, mildly annoying nerd with no genocidal ambitions, although he does have a dark side.
No Social Skills: Not in the "Good lord, were you raised by alien robot wolves?" sense, but he's suffering from a bad case of adolescent pretentiousness and he lacks tact.
Sugar and Ice Personality: He's not the most approachable of individuals, between his social awkwardness, overly-serious manner, and sheer size, but he's kind in his way and has a STRONG desire to help people.
Team Dad: Rose even tells him that he'd make a good parent in one story.
Badass Adorable: Doesn't often get a chance to show it, but he's had his moments.
People who really know him will also talk about the time he went jousting at the local renfest and unhorsed every re-enactor that dared come up against him. And then broke his nose on the dismount. There are photos on the internet of Tavros Nitram smiling and throwing the horns, grinning through a curtain of crimson from both nostrils and both eyes already swelling up, surrounded by astonished and horrified people in corsets.
Dark and Troubled Past: He's doing quite well now, but in the past he's faced homophobia, bullying, depression, a permanent spinal cord injury, and a (failed, obviously) suicide attempt.
Friend to All Children: He's specializing in child and adolescent psychology, and his character introduction mentions that he gets along well with younger people, although they tend to think he's kind of a dork (probably because he is a dork).
Bunny-Ears Lawyer: She's the same cackling weirdo she was in the source material and once spontaneously ran off the grounds to locate and institutionalize Stephanie Meyer, but is still a mature and effective therapist.
In-Series Nickname: "Doctor Tongue", she was also called "Tiny Asian Doogie Houser" by her college buddies.
Improbable Age: 34, which isn't too far fetched for a psychologist, but being chief of staff for an entire institution is (which is lampshaded).
Noodle Incident: The incident that spawned her aforementioned "Doctor Tongue" nickname. She thinks the rumors are hilarious.
Rummage Sale Reject: There are several references to her wearing colors that clash badly or outfits that just don't go together, but people cut her some slack due to her blindness. It's also implied that she may be doing this intentionally. According to Equius:
Her dress is awful, teal and vivid red, and you suppose she chose it for the loudness of the colors. You have no idea where a woman might buy something so terrible. Surely no company would deliberately create such a dress, not that it is any business of yours.
Animal Motifs: Fish, of course. Her father was a crab fisherman and Deadliest Catch is her favourite show.
Plucky Girl: Most likely, although she hasn't made enough appearances to know much about her personality. Her intro mentions that she "rules the front desk with an iron fist" and is capable of taking on Feferi.
Hidden Depths: While he's built up as a reprehensible toolbox for most of the AU, it's hinted here and there that he feels guilty over what the separation is putting Dave through, and does recognize on some level that he's an unfit parent.
Lethal Chef: His meals are inedible slop cobbled together from whatever's lying around, which is why Dave got into the habit of stashing food wherever he went.
Man Child: Deconstructed. Bro's a single parent in his early thirties with the apparent maturity, responsibility, and domestic aptitude of a teenager, and this affects Dave badly.
Not as You Know Them: Word of God is that in this AU, Bro and Dirk are two different characters. There is a level of Early-Installment Weirdness at play here, since this version of Bro was created before Dirk was introduced and based on an interpretation of Bro that has little in common with Dirk.
Parental Neglect: Leaves Dave home alone for hours or even days at a stretch, convinced that the kid can take care of himself. Dave has often gone without food and accidentally injured himself and had nobody to care for him.
Really Gets Around: Makes his living through homemade porn, both puppet-related and traditional. And that's not counting his lengthy series of girlfriends.
Abusive Parents: Actually subverted, according to Word of God. Mrs. Lalonde is well-intentioned, but wasn't prepared for a daughter and doesn't know how to raise her. As with the source material, a lot of her abuse and neglect is actually due to Rose's warped perception of her mother and Rona's exasperation with their passive-aggressive spats.