The unmade Helloween was a crossover between Halloween and Hellraiser, and the finale would have transformed Michael Myers into a demonic cenobite. Helloween is a concept that was briefly taken seriously in the aftermath of Freddy Vs Jason's box-office success in 2003 but was ultimately scrapped. Halloween is a franchise that has lasted for over 40 years and counting, and while the quality of the films has varied wildly, Michael Myers - AKA The Shape - is still an iconic slasher.
Clive Barker's Halloween hit screens in 1987 and was an adaptation of the author's own The Hellbound Heart. The movie's graphic horror and memorable villains made it a surprise hit, and it makes a great double-bill with sequel Hellbound: Hellraiser II. While fans of the Halloween saga will debate the merits of the various sequels or Rob Zombie's divisive Halloween movies, the Hellraiser series took a serious nosedive following 1992's Hellraiser III. There are ten movies in the original series, with the last six having gone straight to video. Of those STV series, only Scott Derrickson's Hellraiser: Inferno or Hellraiser: Deader is of any real note.
Freddy Vs Jason - which final girl Lori really won - famously spent about a decade in development hell, with countless concepts being rejected. The potential of the crossover raised a lot of excitement in the horror community, and filmmaker Dave Parker - having realized that Dimension owned both Halloween and Hellraiser - pitched them on a movie he dubbed Helloween in the late '90s. This would have revealed Michael Myers was possessed by a demon named Sam Hain who escaped from Hell, and Helloween would have seen Pinhead and the cenobites come to take him back. In the finale, Michael Myers himself also would have become a cenobite.
Just like Dr. Channard learned firsthand how cenobites are made in Hellbound, Michael would have been subjected to the process in Helloween. According to an interview in the book Taking Shape II, the Michael Myers (AKA The Shape) cenobite would have had his mask permanently affixed to his skin and had his arms replaced with knives. Parker's Helloween pitch did a surprisingly good job of combining the mythology of both Halloween and Hellraiser, giving Michael a new origin story while bringing back Hellraiser hero Kirsty Cotton.
Parker's Helloween was rejected at the time, as Freddy Vs Jason was still years away and Dimension wasn't interested in combining the franchises at that time. Ironically, following Freddy Vs Jason, Dimension managed to briefly attach Clive Barker and John Carpenter to a potential Helloween movie. Halloween producer Moustapha Akkad would personally nix this, however, feeling the combination didn't work and that the ailing Hellraiser series needed Halloween more than they needed it.