Lily
Lily Reynolds
Played by: Anya Taylor-Joy
- Eerie Pale-Skinned Brunette: Lily has pitch-black hair, paper-white skin, and spends most of the film contemplating murder. And she goes through with it.
- Foil: Lily is one for Amanda. Amanda is an Emotionless Girl who compels Lily to murder Mark, while Lily is shown to be the more emotionally-driven of the two. By the end, Lily is colder, while Amanda is finally shown emoting.
- Karma Houdini: Lily gets everything she wanted.
- Spoiled Brat: Although she tries to deny it, Lily sometimes acts like she is entitled to a better life than others. Her unwillingness to give up her privileged and sheltered lifestyle by going to boarding school forms a large part of her motivation to murder her stepfather.
- Stepford Smiler: Lily herself is a highly dramatic version. She responds extremely - and violently - if Mark ever threatens to blow her perfect façade.
- Villain Protagonist: She is the main character alongside Amanda.
- White Anglo-Saxon Protestant: Lily is a classic example, though she denies being a snob.
Amanda
Amanda
Played by: Olivia Cooke
"It's not that I'm a bad person. It's just that I have to try harder than everybody else to be good."
"You cannot hesitate. The only thing worse than being incompetent, or being unkind, or being evil, is being indecisive."
- Asshole Victim: Amanda is a deconstruction. She's an asshole by her own admission, but the end is, at best, bittersweet for her.
- Emotionless Girl: Amanda is completely unfazed by everything and generally creeps everyone out, though she argues it doesn't make her a bad person.
- Foil: Amanda is one for Lily. Amanda is an Emotionless Girl who compels Lily to murder Mark, while Lily is shown to be the more emotionally-driven of the two. By the end, Lily is colder, while Amanda is finally shown emoting.
- Sociopathic Hero: Amanda clearly suffers from some kind of antisocial psychological disorder, but she is the more sympathetic of the two girls. Early on in the film, she outright states that not feeling emotions doesn't necessarily make her a bad person, it just means she has to try a little harder than everyone else to be good. In the climax, she makes a Heroic Sacrifice by willingly finishing her drink despite knowing it's been Roofied and taking the blame for Lily's murder of Mark.
Tim
Tim
Played by: Anton Yelchin
- The Aggressive Drug Dealer: Tim is a wannabe drug dealer with delusions of grandeur. He only sells to children, and aggressively tries to push his merch at a teen party even after being asked to leave by the guests.
Mark
Mark
Played by: Paul Sparks
- Abusive Parents: Mark is Lily's step-father, and while he largely refrains from physical violence (aside from grabbing her wrist once), he displays some blatant emotionally abusive behavior towards Lily, insulting and belittling her at every opportunity.
- Asshole Victim: Mark. While he mostly refrains from physical abuse to Lilly, he's so rude, nasty, and aggressive that it seems unlikely anyone will feel any sympathy for him even after Lily kills him.
- Jerkass: Mark is such an asshole that viewers are likely to agree with Amanda that the world would be better off without him.
Cynthia
Cynthia Reynolds
Played by: Francie Swift
- Stepford Smiler: Cynthia is a much calmer version than Lily, as while she seems obsessed with making her cruel husband happy, she doesn't do anything actively malicious to achieve this.
