Vriska Serket, also known by her Trollian handle arachnidsGrip, is one of the trolls. Her associated zodiac sign is Scorpio (♏) and her horns are shaped like a claw and a stinger.
Vriska is, more often than not, a huge bitch. She gets easily bored, makes shady deals with people, does horrible things to her "boring" friends, and then slams herself because nobody likes her or - even worse - hates her enough.
Much like her lusus, a massive spider, Vriska often manipulates others, even going as far as paralyzing Tavros and trapping him in her web for her to feast upon.
Vriska believes that bad things constantly happen to her because she has terrible luck. Kanaya Maryam and Doc Scratch suggest that her own behavior is more likely the cause - for example, she constantly steps on d4's only because she leaves them all over the floor instead of tidying up. She also seems to hold some degree of distaste towards her own blood color, mockingly referring to it as "enviable cerulean swill" - just another thing for her to blame her problems on. On other occasions, though, Vriska holds herself in high regard - she often brags about her exploits in Flarp, or just about herself in general.
While she sees herself as a great manipulator, it seems that she is often manipulated herself, as clearly evidenced in Doc Scratch's final conversation with her. Although she would loathe to admit it, she envies Terezi a great deal because of Terezi's ability to manipulate people without the use of psychic abilities. This could be a possible motivator for Vriska, as she attempts to trick, deceive and backstab nearly every other troll - perhaps as a way to prove herself in Terezi's view or even in her own. When another troll calls her out on using mind powers, she either denies it to the point of absurdity or throws a tantrum.
She was responsible for putting John to sleep before he could prototype one of the Distinguished Houseguests (which was coincidentally a blue doll missing an eye and an arm, similar to herself and Jack). Because of this, she believes herself to be responsible for Jack Noir's fourth prototyping, and thus his attack on the trolls' session, and claims to have intentionally done so as she wants to be the one to kill him. She tries to justify herself by claiming that it had to happen to prevent a doomed timeline. Although since avoiding this event was one of the few possible between-universe travel paradoxes, instead of just a time paradox, it is unclear whether it would have caused a doomed timeline, or something else entirely. According to Karkat and Aradia though, paradox space forces these events to be unavoidable.
Despite all her negative traits, she does have a softer, more benevolent side. She was genuinely upset when her plan to reconcile with Aradia failed, and she also has admitted to John that she felt bad about killing Tavros and that even though her methods were more than questionable she did genuinely try to help him get stronger. She also mentions to John that one of the reasons she wants to fight Jack Noir is to protect her friends.
After her murder of Tavros, Vriska admits to John that she feels terrible about it. According to troll culture, she had every right to kill him, and claims she can't tell the other trolls how she feels out of fear of seeming weak. She seems to have always felt bad about ending up as screwed up as she did as a result of troll culture, and laments how much better humans have it. However, this is more remorse towards herself, rather than guilt for any of her other atrocities, most likely because she despises her own existance as a troll, to the point of saying troll society was better off dead. She also willingly admits that there is a good chance she will die if she fights Jack Noir, but considers Jack being stopped far higher priority than her own life.
She seems to have lost some of her faith in having all the luck, but decides she has to go after Jack regardless, seeing her fight will have to mean something, and relying on luck, instead of inner strength and bravery, would be meaningless.
Vriska cares for her friends more than she usally admits, stating to John that protecting them was her real reason for planning on killing Jack, not just glory. She was known here to get anrgy at Jack for killing KARKAT and TEREZI after seeing their corpses in a doomed timeline.