Over the course of writing and revising the tetralogy, I came up with background details to better flesh out the universe of Friday the 13th Reimagined. Some of these details were implied in the final scripts, while the rest are being revealed for the first time.
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How the Lenape dagger came into the possession of the Crystal Lake Lenape's been lost to history. Metallurgy was unknown to the Lenape, so they weren't the original fabricators. The Lenape claimed it was gifted to them by the manitowak, the life-spirits of their mythology. Skeptics scoff at this, positing instead that the dagger was of Mesoamerican or possibly even Andean origin and had gradually made its way north to be acquired by the Lenape through trade, though the dagger doesn't closely resemble anything made by the cultures of those regions. The shamans of the tribe used the dagger in their magic ceremonies, both to facilitate good fortune and ward off evil, though its power wasn't absolute, as it failed to protect them from the emissaries of the Dutch West India Company who exterminated them.
After displacing the Lenape, Sjaak van Voorhees made his fortune and became patriarch of one of the first prominent families in the region, possibly using the magic of the stolen dagger to influence his luck. In spite of this material boon, the van Voorhees family would come to be cursed with personal misfortune, with infidelity, illness, violent/premature death, etc. afflicting each of Sjaak's descendants up to the 20th century. In the 18th century, the Voorhees family lost its fortune. By the time of Elias Voorhees' birth, the Voorhees' were just another working class family, their wealth an old memory. The Lenape dagger remained in the family's possession, an heirloom, along with Sjaak's journals, which told of his sins and the dagger's power.
Elias Voorhees, born 1922, and Pamela Voorhees, born 1930, were third cousins. She may not even have yet turned sixteen when he got her pregnant out of wedlock. After finding out, Pamela's parents disowned her and kicked her out of their home. Elias was initially intent on marrying her. However, Pamela gave birth to Jason after only six months pregnant. Although a normal-looking and healthy baby, it became apparent Jason was autistic. Not wanting to be saddled with an intellectually disabled child, Elias left his fiancée and infant son, relocating to a neighbouring county where he took a job as a forest ranger, eventually marrying another woman and fathering a daughter. Following Elias' abandonment, the Christys, a devout Christian family in the ways that matter, took Pamela into their home, helping her raise her disabled son, even giving her a job as camp cook during the summer months. Their son, Steve, was provided as a playmate for Jason. Jason loved Steve dearly, though it's debatable how much Steve reciprocated.
Crystal Lake once had an operating zinc mine. One of the miners was Joshua Sundin, who'd lost his right eye in an accident some years back and taken to wearing an eyepatch. In February 1946, after the zinc deposits were exhausted, the mine was closed and Josh laid off. Seven months passed with Josh failing to find new employment. Having never shied away from domestic abuse, his treatment of wife and child absolutely deteriorated as their savings dwindled, his violent outbursts coming in mounting frequency and ferocity. Finally, in September 13 of that year, he murdered his family in a fit of rage. Immediately remorseful, he chose to commit suicide. Rowing out to the middle of Crystal Lake, he put a chain fastened to a heavy rock about his neck and tossed himself overboard. He successfully drowned, but in his violence and grief, Josh was found to be a perfect vessel for the wrath of the Crystal Lake spirits and they returned him to life. He'd lost his eyepatch in the lake, so coming ashore, he acquired an empty burlap sack, made an eyehole, and put it over his head to conceal his shame. He then snuck away to the abandoned zinc mine, languishing there for two months. Once he reemerged, he attempted to exhume the bodies of his wife and child from their paupers' grave, but was caught in the act and chased off. Incensed, he embarked on a six-day killing spree across town, committing necrophilic acts upon many of his female victims. His rampage came to a close when the police chased him down to an abandoned shack in the woods, where he was gunned down.
Elias eventually learned of Jason's death some months after the drowning. Having harboured guilt for abandoning Pamela and their son, Elias felt time was overdue to make right by her. He told his wife of the family he'd abandoned; she promptly left him, taking their daughter with her. Returning to Crystal Lake, he met with Pamela. Having acquired a small fortune in the intervening years, he offered to give her child support back payments; she rebuffed him, wanting nothing from him and nothing to do with him. Elias was determined to redeem himself. Using the Lenape dagger in tandem with a spirit board, Elias began trying to channel his late son. He was successful in making contact with the collective consciousness of the Crystal Lake spirits. Jason was with them, soul and body. They were willing to return him in exchange for two others; Elias agreed. A year to the day of Jason's drowning, Elias performed the resurrection ritual according to the spirits' instructions. He murdered Barry and Claudette, beheaded them, and tossed the heads into Crystal Lake. Jason's body, which'd spent the past year putrefying at the bottom of Crystal Lake, was reconstituted and sent up to the surface.
Upon being greeted by Jason the night of his resurrection, Pamela saw only a malformed subhuman creature at her doorstep and reacted accordingly. Startled by her screams, Jason fled into the woods. Shortly thereafter, he saw his own reflection and realized why his mother had reacted the way she had. The spirits had taken no care restoring his face, tongue, or vocal cords when they reanimated him. Unable to return home, he spent the next several months living in the woods alone. He never got hungry or thirsty, was unbothered by temperature extremes, and whatever injuries he acquired healed quickly. Though angered by his plight, with the voices of the lake goading him to take his frustrations out on his mother and the locals, both his love for her and the social anxiety from his disfigurement kept him from lashing out. He kept close to home, so he could continue to see Pamela from afar. He was spotted often enough by the townsfolk to become a topic of speculation and gossip, even earning articles in the newspaper. Pamela eventually put two-and-two together and realized this boy-beast was her son. Coaxing him out into the open, she took him back into her home.
Pamela kept Jason homebound to protect him. But Jason began sneaking out, and when he returned, Pamela would sometimes find him stained with blood. Reports of young children going missing and the occasional mangled corpse found in the woods appeared in the paper, and Pamela realized what Jason was getting up to. She began locking Jason in his room for everyone's protection. As Jason grew older, he grew stronger. When he broke his bedroom door down to get out, Pamela began locking him in the basement. Then after Jason broke the solid oak door down, she had a steel door installed. For a time that seemed to do the trick. Then Jason found another means of getting out of the house. Pamela was perplexed, as there was no other door to the basement. Examining the basement, she realized Jason was using the old well as an escape route, worming his way through the dried-up water channel to freedom. Finally she had Jason chained to the floor, and that stopped the breakouts for good. Though afraid of Jason, Pamela continued to love him, and she spent as much time down in the basement with him as she could. Jason could've killed her at any point, but his love for her was so great, even the voices of Crystal Lake, shouting in his head, couldn't coerce him into harming her.
In the years after the 1984 Crystal Lake massacre and Tommy's institutionalization, Trish turned to hard drugs to cope with her trauma, especially heroin. Trish then met Dory, a lesbian who volunteered at a local woman's shelter. After becoming friends, Dory helped Trish get clean. During this process, Trish realized she was bisexual and fell in love with Dory. Trish took to bodybuilding and martial arts as alternate coping mechanisms. She became a bounty hunter out of a drive to pit herself against dangerous men and prove her mettle in combat. Though moments of great stress would cause her to briefly relapse, she managed to quit heroin for good after the events of 1990. She eventually quit bounty hunting, choosing a career as a personal trainer and occasional model. Trish and Dory continued their relationship, eventually becoming a throuple when Dory consented to Trish having a boyfriend.
Sheriff Garris survived. He falsified evidence that Elias had kidnapped Tommy from the hospital and committed Tommy's murders, exonerating Tommy.
Tommy continued to suffer PTSD and depression after being freed of the Crystal Lake death curse. He remembered everything he experienced while under the influence of the spirits, the face of each person he'd killed. He made a number of suicide attempts, but with his family's support, he managed to persevere. He relocated to Springwood, California, where he took a job as a paramedic before eventually becoming a physical therapist.