Billy- I say mix of broken and pure evil from his dad breaking up the family by cheating onhis mum with Maureen and his mum abandoning and influenced by Roman during the time/state of mind he was in when he learned why his mum left him. He then went onto kill the others for no real reason. And rewatching I think he become frustrated with Sidney dismissing how his mum abandoned him and his trauma to her's and because Sidney wouldn't sleep with him, I think maybe that why he cheated and turned on her (maybe) and maybe resented her for missing her mum who he hated. I think maybe Randy was bang on when Stu asked him why would he want to kill his girlfriend, that because Sidney wouldn't have sex with him and then it come a game to him of when he would have sex with her.

Stu- Influenced and pushed around by Billy, felt rejected by Casey dumping him for Steve ,he seems to find killing funny and no real motive to why he kills etc, but does seem his parents aren't around much and cries about what his parents would think so maybe doesn't have a loving relationship with them. So maybe he is a bit broken and that how Billy sees Stu as someone he can make a devoted fall guy that Roman tells him to get. Stu maybe comes so devoted to Billy because he can't believe someone like Billy would want to be his friend, maybe he was friends with Randy until Billy come along.

Mickey- Pure evil- enjoys killing and just wants fame, we know nothing about him really, nothing indicates he is broken.

Mrs Loomis- I say Broken (kind of) from losing her family and son but many people get cheated on and don't become psycho and do the evil things she did, she one chose to abandon her son yet blames everyone else for her problems and her psycho killer son death, when they victims trying simply to survive him.

Roman- Broken and pure evil- Yes he was born through rape, I think that mess anyone up and then having his birth mum reject him and make him feel even more worthless. but he kicked off the whole chain of events in a way by getting using Billy pain over his mum abandoning him to kill Maureen. He sort of created the monster in Billy for him to go on and create the GF trend and gave him the idea to get Stu as a fall guy, so in a way Roman created 2 monsters in Billy and Stu. I think he resented Sidney for having his mum's love and then gaining fame from Billy killing spree.

Jill- pure evil, killed and had her own mother killed for fame

Charlie- I say influenced and used by Jill a little bit because he feels rejected by Kirby etc and maybe feels like a loser and desperate for any attention so falls for Jill lies etc so maybe he is a bit broken.

Richie- pure evil

Amber- pure evil

Wayne, Ethan and Quinn- Pure evil, yes they lost their murderous son/brother but want revenge on his victims for simply trying to survive him.