You're going to kill me, KB, but I have to be the haughty, detail oriented horror geek I am. "The Final Chapter" was the 4th Friday the 13th film, whereas I think you're thinking of "Freddy's Dead: The Final Nightmare." In Freddy's Dead (arguably the 3rd best film of the series, behind the original and part 3), as the people of Springwood are torching Fred Krueger following his trial dismissal, Incan Dream Demons come to Freddy and offer him the power to be immortal and haunt the dreams of the living. He is offered this power due to the fact that the Incan Dream Demons can only exist in the evilest soul.
In Halloween: The Curse of Michael Myers (the 6th installment, starring Paul Rudd), it is revealed that Michael has been infected with the Thorn curse, which is the English translation for the word "Thurisaz." It has Norse roots as well, since the "Thurse" were the minions of the Norse God "Thor." The runic curse itself dooms the infected person to kill his or her family as a sacrifice for the good of the entire tribe. This is why, in Halloween 4, Michael remains comatic until during the scene in which he is being transported from Smiths Grove Sanitarium to Ridgemont Sanitarium. Michael is docile until one of the EMT's mentions that his only living relative is a neice in Haddonfield, which causes Michael's rage to return and the killing spree to recommence. It can be speculated that he remained comatose with the belief that the explosion at the end of Halloween 2 killed his only other living relative, Laurie Strode.
The folks at the Halloween franchise did some fantastic research for Halloween 4-6. The Thurisaz rune is in many books and works ranging from occultism to simple mythology, and to use it to explain Michael's unquenchable killing instinct, I felt, was genius. It's just too bad all of that research and writing took a back seat to bullshit teeny bopper horror (thanks, Scream!) and in H20, all three of those films were treated as though they had never happened.
