Michael Myers: He didn't murder his sister when he was 6. Instead, he grows up fairly normally but is very quiet, rather emotionless, and apathetic. He eventually gets a job working as a mechanic. On Halloween night, 1978, Judith Myers went on a date with her boyfriend, who had been drinking and caused a car crash. He survived, but Judith did not. Michael seemed hardly upset about this, although of course, everybody deals with grief differently. Shortly after, the boyfriend went missing and was found dead nearby. As time goes on, people forget about the mysterious murder, and the killer is never caught. That is, until more and more corpses are being found each night, and each victim is somebody who mistreated Laurie recently. The basic gist is that Michael isn't actually emotionless, but is actually rather chipper and excitable, but only when committing acts of violence, which he doesn't do because that's not a normal thing to do. Then, when his sister dies, he finally lets out his violent nature and gets addicted to it, looking for any old excuse to murder people, typically choosing people who "hurt" his younger sister.

Jason Voorhees: He didn't drown as a child. Instead, he grew up and became a camp counsellor at the camp he loved as a child. Aware that he looked frightening, he chose to wear a sack over his head instead of a prosthetic. Even though he didn't go missing, Pamela's mental health still plummeted, and she raised Jason with the notion that bad people deserved to be punished. Jason, being a mentally challenged man who sees the world in mostly black and white, takes this to mean that it's up to him to deal with bad people. Thus, during his time as a camp counsellor, he is well-liked among the children, but whenever a teenager or adult does something "bad", Jason dons a hockey mask to "cover his identity" (he's a bit slow), and he kills them. He's not malicious or a serial killer, but he is still murdering people for the most minor things. For example, if he saw somebody harassing a woman, he would brutally murder the harasser. Is this kinda just a rehash of Angela Baker? Sorta.

Sadako Yamamura: She didn't die in the well. In this case, when she was pushed down the well, just like in canon, she survives the initial fall. The difference is that, because she is knocked unconscious and appears deceased, her father doesn't put the cover over the well, and instead leaves her to rot. Of course, Sadako did survive and then began her crawl out of the well. In canon, she couldn't get the cover off and slowly died inside, but because the cover wasn't put on, she managed to crawl her way out. Bitter and vengeful after this attempt on her life, and also every other tragedy to her name, Sadako decides to get revenge and use her psychic abilities to kill everybody who tormented her. She still gives out heart attacks, but the difference is that instead of being a ghost haunting a videotape, killing poor victims, she is specifically going after everybody who hurt her, and she gets to live afterwards. Very Kill Bill.

Ash Williams: Ash does get possessed. When the Necronomicon is read from, Cheryl goes to bed early, and the only people still up are Ash and Linda. When Ash is preparing to give Linda the necklace, he instead hears somebody outside and goes to investigate. Because of this, instead of Cheryl being the first deadite and the main threat, it's Ash who becomes possessed. He murders and turns all of his friends into deadites, and the only survivor is now Cheryl. Cheryl does manage to get rid of most of the deadites, but can't kill Ash. Ash then murders Cheryl, but before he can go and cause more havoc, the sun rises, and he returns to "normal." He regains his humanity, but it turns out that he is permanently "half-deadite". He can do anything deadites can do (float, grow claws, possess items), and he always has Evil Ash yapping in his ear, but he himself is still in control. He realises what has happened to all of his friends, and that it's his fault, and then he decides to grab the book and make sure nobody else ever reads it and starts it up again. He is still the Chosen One and still goes out and deals with deadite threats, but the difference is that it was he who started it all. That and because his face is always half-demonic, he can't at all interact with human society, and has to hide out in the woods as a local boogeyman urban legend.

Charles "Chucky" Lee Ray & Tiffany Valentine: Charles doesn't permanently become a doll. This one's probably my most "out there", but I had a funny idea. So in this AU, Tiffany Valentine is actually Karen Barclay's sister, making Andy the nephew of Chucky and Tiffany. The Barclays are also wealthy. Charles and Tiffany are not serial killers, but they are not good people either. Tiffany used to be rich but wasted all her money and is now living in a trailer with her husband. Jealous of her sister and bitter that her sister is "not helping her with money issues", Tiffany wants nothing more than to murder her and take the inheritance. The only issue is that the money would go to Karen's son, not her. Well, it just so happens that Charles has a voodoo amulet that he can use to transfer his soul for some reason, and together the couple come up with a plan. The idea is to have Charles briefly possess an item that is similar enough to a small child, and then murder Karen in that form, so that Andy is blamed and is sent away, and then Tiffany will get her sister's wealth. The couple decide he should have a Good Guy doll, as it's a similar size to Andy and a popular toy they could disguise as a gift for the child. So Charles links his soul with the toy; that way, he can switch back and forth at will, and either be in the doll or back in his human body in a different location. On Andy's birthday, Tiffany gifts him the doll, and then the plan is set in motion. Basically, Charles possesses Chucky, but he can switch back and forth at will. Funnily enough, I imagine their dynamic to be very similar to Harry, Marv and Kevin in Home Alone.