Vriska has some slytherin tendencies, but what puts you in a House appears to be some combination of “what do you want?” and “how will you go about getting it?”
What does Vriska want? To save the day. Loudly. Rules? Fuck ‘em, they get in the way of being a hero. and oh, what a hero. no one else on the Hogwarts grounds has the stones or to challenge her for Biggest Loudest Dickbag.
Glory WILL be hers. She will be the very best. she will win all of quidditch games, all of them.
She’s brave, she’s brash, she fears almost nothing. She’s also dumb as a stump. She gets away with so much shit that she shouldn’t, and everyone just sort of lets her take the spotlight even when it makes no sense, because she’s a Gryffindor, and if you get in her way, she will kick you off the stage on her way to claim the trophy for Best Character Ever, and everyone will just sort of pretend it was an accident, even though they know it wasn’t.
she gets away with using the unfortivable curses on her friends and enemies to ensure her rise to power for way longer than she should have, because no one wants to believe such a shining star, and certainly no Gryffindor, would be a Death Eater.
and she’s not.
she plans to take Voldemort down, and she wants to do it singlehandedly.
I have never been able to accept slytherin Vriska for basically this reason. She’s James Potter with spiders.