Friday the 13th (film)/WMG

The events of Jason X were a dream created by Freddy to test Jason.
Before using Jason to his advantage, Freddy wanted to know just what Jason was capable of. This explains both why Jason X was released before Freddy vs. Jason, and the ridiculousness of the premise.

Jason doesn't actually come back to life at the end of the remake, it's a bad dream

 * Whitney dozes off, relieved to finally be rid of him. Then WHAMMO! nightmare.

Jason is a stoner.
In the last movie, he seems intent on killing teenagers that take weed from a large patch in his woods. That's HIS weed. (This theory comes from the movie review at spill.com.)
 * Alternatively, Jason's a drug dealer. Not everyone who farms and sells weed is a user; it could be all business for him. Those little shits are stealing his weed and costing him money.
 * Alternatively-alternatively, Jason's neither of these things; the weed is bait. He planted that patch knowing that teenagers would be drawn to it, and inevitably smoke it, making them easier to kill.
 * That... actually seems very plausible.
 * Jason may not be as dumb as he seems.

The kids sent to Crystal Lake have been sentenced to death
All the kids are violent criminals. They are brainwashed and sent to Crystal Lake, and hidden cameras record their grisly execution for the masses. Jason is a convicted murderer who was promised life instead of the chair if he offs all the kids. This is why Jason keeps coming back from death; there's more than one Jason, and they all take the same deal.

This also explains why the kids are so dumb: they are conditioned to run off by themselves.

And finally, 'Jason' gets luxury dinners if he kills off the kids in a certain way; the viewers of the surveillance tapes expect the cliches of a horror movie.
 * Alternately, since being able to give people false memories like that would probably imply that this is the future, Jason could be a bio-engineered killing machine. He keeps coming back because when he has a very resilient physiology and can hibernate for very long periods, and if he is killed for good the government just uploads all his memories, clones him, and put the memories in the clone. He may be brainwashed to believe his own origin story. Or perhaps his origin story is actually true, except he was brought back to life and transformed into the Jason we know by the government.

The telekinetic girl the seventh film was a relative of Carrie
They both have mental powers, they both are messed up, and the book did say the gene for telekinesis only expressed itself in females.
 * The movie as a whole is a lot more entertaining if we just pretend it is Carrie.

All the films after the original are just a delusion of Mrs. Voorhees.
Only the relatively realistic events of the first film ever happened. Jason did die as a child and never came back to life. Mrs. Voorhees, incurably insane after the loss of her son, imagined him coming back and taking vengeance on camp counselors.

He always dies because that's the event in his life that she most remembers. But in her fantasies, he always comes back. Just before dying, she became so delusional that she re-imagines the recent events with Jason as the killer instead of her (the 2009 remake).


 * Specifically, the films all zip past her as visions in the seconds while she clutches at the space where her head used to be after getting decapitated at the end of the first film.

Jason is some sort of corporeal ghost.
It'd explain a lot. Jason actually did drown as a kid, with his restless spirit residing in the lake. The death of his mother angered his spirit into taking vengeance, but as A. a ghost and B. a mentally handicapped kid, his targets are basically "anyone who crosses my path." He generated a corporeal, hulking body and set off to avenge his mother. As killing is really his only purpose, it's the only thing he can fully comprehend - this is why he can be so creative with his killing methods despite being dumb when it comes to anything else. The people who "killed" Jason throughout the series only managed to trick him into thinking he was dead (well, dead in the not getting up and killing people way) - once Jason remembers he's a corporeal ghost and thus can't die, he gets back up and starts killing again. This also explains how he's able to pull off the classic offscreen teleportation trick, as well as how he managed to string up people's bodies in gruesome ways with so little time.
 * Well, he *does* escape from his private hell when Freddy, invading his mind in the form of his mother, reminded him that "you cannot die; you are only sleeping."

The reboot film is in the same continuity as the live action Transformers films.
Trent appears in both films. Friday the 13th was produced by Michael Bay. There isn't much to elaborate on.
 * Which implies that a Freddy vs. Jason vs. Optimus Prime crossover might occur, the prospect of which will make any child of the Eighties squee uncontrollably.

Jason is a zombie ressurected by Pamela
One of my fave theories I had heard was that Jason is actually just a demon possessing the dead body of Jason Vorhees who was trapped in that by Pamela's experimentations with dark magic after her sons death. This was brought up in the sadly non-canon comic book Freddy vs. Jason vs. Ash where it's either hinted or flat out stated (don't have the books in front of me) that she used the Necronomicon and turned her sons corpse into a kind of deadite.
 * Alternatively, Jason's powers are a result of Pamela dabbling in black magic. She used it either in an attempt to simply bring back her lost child with the unusual strength and immortality being an unexpected side effect, or fully with the intent of making him large and extremely powerful, unable to die so that he can kill those Pamela felt were responsible for his death. What she didn't know was that the spells don't work until the conjurer's death.

Jason was a Metahuman from birth with a limited Healing Factor and rapid evolution powers. He has been "undead" since he drowned in Crystal Lake and washed ashore.
When Jason was dealt the final blow by Ginny in Part II, it was actually fatal...or would have been, were it not for the latent healing power that resurrected Jason after he drowned years earlier. Each time Jason has been killed, his healing factor not only revived him, but gave him new abilities, including Super Strength that increased with each death (starting with part III), Invulnerability (Part VII), and teleportation (Part VIII). In Jason Goes to Hell, Jason was blown up, but his healing factor was on a cellular level, and generated the "Hellbaby" over the years to act as a backup body to seek out fresh genetic material for a new body, explaining his more human appearance in Freddy Vs. Jason and Jason X. Also, Jason gains a more intuitive intelligence, allowing him to improvise more weapons in lieu of his famed machete and know to render vehicles immobile and sever power and phone lines.

The drawback to Jason's healing power is that it sacrifices complete restoration in favor of durability and pragmatic evolution. This explains his different appearance in each movie; In Part II he looked the most human, in Part III his head had lost hair and his face began to degrade, and in Part IV he began to become more noticeably decayed in appearance. Jason's time buried in his grave between the end of Part IV and the start of Part VI restricted his ability to regenerate, hastening his transition into an "undead" form.

In addition to jump starts from electricity, Jason's powers are triggered by an ability that is also a "blessing" and a curse for him, this being his limited telepathy. This power to sense thoughts was triggered when he was revived by his healing powers, and are the reason for his decades long seclusion. On the night his mother Pamela was killed, the thoughts of lust and disorientation from being intoxicated were the strongest things he had sensed earlier that day, and he associated them with his mother's own thoughts of revenge before her death. When decadent thoughts become strongest, it accelerates his healing factor and revives him more quickly. This is coupled with an enhanced sense of smell which allows him to track people more easily. The smell of pheromones and weed smoke also send him into a rage due to association with his mother's killers.

Jason's telepathic abilities also allowed him to form a link with Alice, letting him track her to her home and murder her. Alice's hallucination of Child-Jason pulling her into the lake was the moment this link was formed by a then adult Jason. The formation of psychic links with others also have an effect of reviving Jason, as evidenced with Tina in Part VII, Rennie in Part VII Im and Freddy Kreuger.

Jason keeps a bunch of animals on hand to distract his victims.
This happens a lot. Someone hears a noise. It's a slasher movie, so they go to investigate. A cat or dog jumps out. The person relaxes. Then Jason pops up behind them and sticks an ice pick in their head, or pulls them out the window. Seriously, this happens so often he must keep a bunch of animals in his pocket, using them to lull his victims into a false sense of security after the initial Cat Scare has passed.
 * Well, it does look like a hand throws the cat through Alice's window in Part 2.

The sewer worker killed by Jason at the end of part VIII was Ed Norton.
After all, it takes place in New York City, and Norton is much older because over 30 years passed since the series.

Jason never drowned in Crystal Lake in 1957.
He in fact managed to splash his way to the shore, but went hiding into woods because in his infant logic he thought he had done something bad. He occasionally steps out from the woods to help his mother in her sabotage missions on Camp Crystal Lake, hiding evidence and indirectly causing some of the damage. This explains how she wasn't caught for over twenty years.
 * Though that would mean she would have known about him being alive, unless her madness led her to believe that when Jason was helping her, it was his "ghost".

The Friday the 13th remake, the Nightmare on Elm Street remake, and the Rob Zombie Halloween remakes take place in the same continuity.

 * Because why not?

The remake isn't a remake at all, but another sequel.
Any previously established continuity that it contradicts can be easily explained away:
 * Jason being alive instead of an undead Zombie-thing can be explained by it being set somewhere in between part 1 and part 2 (whilst parts 2-4 take place within a couple of days, it is established that quite a bit of time passes between one and two,
 * Him getting the Hockey mask from Barn-Guy instead of from Nebby the prankster (as seen in part 3) can be explained by him having a preference to that kind of hockey mask, and as for him not having the mask in Part 2, in his line of work, he probably loses masks a lot.

Freddy vs Jason actually takes place *before* Jason Goes to Hell
Everyone seems to assume, mainly due to the ending of part 9 and some lines in the Vs movie, that Freddy VS Jason must take place after Jason Goes to Hell. But it actually kind of makes more sense to assume it comes before. For one thing, Steve in Part 9 mentions that the cabins at camp crystal lake were torn down two years prior, yet in Freddy vs Jason we see the whole camp still intact (was it torn down because of the huge explosion that devistated it in VS?) Assuming that Part 9 takes place after VS could also explain how Jason was revived after part 8 (Freddy ressurected him) and how he got from New York back to Crystal Lake (Freddy brought him to Springwood, and then the kids took him the rest of the way back). It might also explain how Jason suddenly developed body jumping abilities, the supernatural ressurection by Freddy ended up giving him some unexpected new powers.

The Events of the movies were all morality testers gone wrong.
Crystal Lake is really a place where people go to test out their sense of right and wrong. Many of the survivors were pure of heart whilst the cannon fod...excuse me victims broke certain rules (mostly horror movie style rules, as well as not being an asshole to the pure of heart.) and die as a result of it. Whomever survives in the end gets an all expense paid vacation. Jason is immortal so he has no problem with people willing to kill him Unfortunately many of the survivors lost their sanity so instead they get a cash prize and their hospital bills paid up.

Jason killed Brenda in part 1
She was lured out with a child-voice calling for help. Also, when Pamela looked at her body, when she asked 'what monster did this,' she wasn't lying to catch Alice off guard. She was genuinely curious because she didn't kill her. Either Pamela's a good vocal imitator, or Jason has been doing some kills without his mother knowing.