Having recently come into a Freddy vs. Jason blank mask straight from the movie mold, I've spent some time studying details to try to get some insight into how it was likely made, and what it's origins might have been.
I can say for sure now that the movie mask was not a ground-up sculpt done for the film. It has a number of characteristics that clearly derive from the Part 6 mask and is almost certainly a third generation re-tool of a Part 6 mask.
The mask has some features that clearly derive from the original Paramount era masks. It has the uneven upper forehead that slopes down to the right, and the slightly askew brow that slopes down in the opposite direction.
The nose is slightly more pointed on the right side of the tip in exactly the same way. The contours are almost a perfect match to my Part 6 (a second gen recast of a movie mask by Fiberglassmasks.com), although the sides appear to have been pulled in for a tighter fit. Though the wonky contours match perfectly, the nose is noticeably smaller than a Part 6 mask.
Looking very closely you can see some finer details that give the recasting away. First, there is the faint impression of a forehead triangle or chevron.
Second, you can see some warping around certain vent hole edges, which can also be seen in some Part 6 masks.
The warping may have been caused by the mask maker working fast and with a high speed on his drill, which might have caused some melting of the plastic as he worked.
Third, you can see that a vent hole on the right side was moved, the circular outline of the original still being slightly visible.
Evidently this was to create a sense of symmetry since the whole placement now matches the pattern on the opposite side of the mask, but why anyone would go to that sort of trouble is beyond me.
While I'd say that the VS movie masks definitely have Paramount-era lineage, it may not have been direct. It's been known among long-time collectors for nearly twenty years that the crew recast one of the earliest fan-made Jason masks, made by a small company called Horror Hockey Masks from 2001 to 2005.
The long-defunct site sold masks that are said to have been cast from a Part 6 mask. And they do have a peculiar characteristic in that some of the earliest copies had that same right-side cheek vent moved outward.
HHM stopped moving the vent hole in later years and sold straight fiberglass castings, so it seems to be a feature unique to the masks sold in 2001-02, around the time Freddy vs. Jason was in production.
Justin Mabry (of Nightowl) said on Facebook recently that he was the first to recast a part 6 mask back in the 1990s, and that his masks were in turn recast by Gates of Hell Studios and Horror Hockey Masks. Here is a rare photo of one of Justin's original masks, currently owned by Bob at Fiberglassmasks.com. This is the mask that my above Part 6 mask was molded from.
A friend of mine and long-time collector sent me an autograph from Bill Terezakis to Joe Cliff of Horror Hockey Masks thanking him for supplying production with a mask, so it looks like that's what happened here. Check it out!
And here is a photo Jo Nobile found at the Ultimate Freddy vs Jason Archive (Facebook) showing what appears to be the HHM mask they were given used during an early costume test.
So in a nutshell, the masks of Freddy vs. Jason were a third generation retool of a mask from Friday the 13th Part 6 via HHM and Nightowl.
This is an interesting shift from what previous films had done, which was to get an older mask or mold straight from Reel FX, who had been custodians of the mask since Part 3, or from a previous special effects team. Evidently things had gotten lost by 2002 and production had to turn to fans as the keepers of the mask.
