But when Burton said he could crank out a script in two weeks, the composer consented to let him try. Why not? If it was good, maybe he'd pass it along to the execs at Fox.

"I said, 'Knock yourself out, but just know there's a 95 percent chance no one is ever going to make this,'" Ottman tells The Hollywood Reporter.

After reading Burton's draft, Ottman was surprised to find himself believing a Beast movie could actually work. He came aboard to develop the project, making tweaks to the script and envisioning it as a $90 million-budgeted spinoff that would also feature familiar characters such as Prof. X and Wolverine — as well as a Danger Room sequence featuring the hate group Friends of Humanity.

The late '80s-set script (read it here) begins in an snow-covered Inuit village that's being stalked by a mysterious creature.

"We wanted to have the tenor of John Carpenter's The Thing where you are in this inhospitable environment," says Ottman.

The script then cuts to Hank McCoy, who is living in the X-Mansion and is keeping his mutation in check with a special serum introduced in 2014's Days of Future Past. During a Danger Room sequence, it becomes apparent Hank is having trouble controlling his beastly nature as he nearly loses control. Early in the first act, we also learn Hank has been helping a scientist who has a similar mutation.

Hank has provided the man with a sample of his serum, but things have taken a vicious turn. Hank goes in search of the man, who he discovers has been terrorizing the Inuit village. The journey all leads to a showdown in which Hank teams up with Wolverine, whom Prof. X has located using Cerebro. The very end of the film ends with a tag revealing the villain Mr. Sinister has been watching the proceedings.

"The idea was we would have Sinister as this multi-film villain orchestrating things," says Burton, who in addition to once working as Ottman's assistant, is a freelance contributor to THR. "We wrote a late-'80s outline of an Omega Red film where the idea is Sinister is testing the X-Men."

Ottman put out feelers to Fox and he was informed that because the script used core X-Men characters such as Prof. X and Beast, it would need the signoff of Simon Kinberg, the filmmaker who was a key architect of Fox's X-Men plans and who was working on Dark Phoenix at the time.

Kinberg politely declined to read the script to avoid becoming unduly influenced by it. Part of Kinberg's rationale was he was thinking of reintroducing Wolverine back into the X-Men world following Hugh Jackman's retirement, so the use of Wolverine in any other movie would only muddy the waters. Ottman had no hard feelings, though by this point he'd become so attached to the idea that he would have pushed to direct the film himself had Fox been interested.

Back when Ottman was reworking the script, he read it from an editor's point of view, trying to pinpoint areas he believed could cause trouble down the road in postproduction. He honed that editor's eye on the X-Men films, and last year earned an editing Oscar for Bohemian Rhapsody.

"It was always in my own self-interest to beg and plead to fix problems that could blow up in my face later. I was also writing 110 minutes of music. I could not afford to have a movie in post that had problems," says Ottman of his days working on X2: X-Men United, Days of Future Past and Apocalypse.

One such change Ottman pushed for came in Days of Future Past. In the original script, Raven (Jennifer Lawrence) comes back to the X-Mansion to talk to Charles early in the film. But as the entire plot hinged on the X-Men stopping Raven from assassinating the villain Bolivar Trask (Peter Dinklage), Ottman worried the audience would be asking why the team didn't just capture her at that point in the film.

He requested a rewrite after seeing the scene filmed, and it ultimately resulted in a scene in which Prof. (James McAvoy) speaks to Raven remotely using Cerebro.

"I said, 'Raven has to be contacted by Charles. Maybe she's at a train station or something, and this is the way he communicates with her without her coming back. She has to be uncontained,'" recalls Ottman. "Simon [Kinberg] wrote a scene with her in the airport. We did that while we were there [during production]. If we had that realization back in L.A. [during post] we could have had to shoot an entire airport sequence. That would have been massively expensive."

Ottman and Burton are sharing the script for Fear The Beast now for fun as the 19-year X-Men saga comes to an end with last weekend's Dark Phoenix. Both note this was still an early draft, and hope it will be judged as such. Had the film actually been made, it would have gone through many more iterations.

"The fact we got the script we got in a few weeks is a testament to Byron, but at the same time every script is ever changing," says Ottman. "As perfect as you think a script is, it will always dawn on you something is illogical or has to be redone."

Read the Fear the Beast script here.