Trivia

The zero gravity scene took sixty-four takes and was shot for two days in a special plane that was lined in padded green fabric covered in reference marks The plane would fly to a high altitude then dive along a parabolic path, falling at the same rate as the gravitational pull. This has been used for several films in the past, including Apollo 13 (1995) 22 years earlier. It was invented by NASA, where it was used for zero-G training for astronauts. Reportedly, a lot of the crew got nauseous during the scene and vomited, except for the main stars, Tom Cruise and Annabelle Wallis, who were really proud of the stunt.

This film was intended to be the first installment in a film universe known as "Dark Universe". Javier Bardem had already been announced as Frankenstein's monster in Bill Condon's 'Bride of Frankenstein', and Johnny Depp was gearing up to play the titular character in 'The Invisible Man'. Other movies planned were 'Creature of the Black Lagoon', 'The Wolf Man', 'Van Helsing' and 'Dracula', as well as 'Dark Army' (where several of the monsters would team up). However, plans for a shared film narrative were canceled after this film was a critical and commercial failure.

When Jake Johnson was offered his part in the film, he loved the idea and the opportunity to work with Tom Cruise, knowing that Cruise does most of his own stunts. He signed on immediately, but when he read the full script and learned what kind of dangerous actions were expected of him, he admitted to getting cold feet. However, Cruise allowed Johnson access to his private facilities for a rigorous 4.5 month training course, making him well prepared for all the stunts he was required to do.

During an interview in April 2021, screenwriter Eric Heisserer admitted that he knew the Dark Universe franchise was doomed from the start when he sat in on the first big planning session with several other heavyweight writers involved. Heisserer, who had been hired with Jon Spaihts to write a reboot of Van Helsing, said that there were "a lot of voices and none of them could agree on much." They couldn't even decide if the monsters should be heroes or villains. He said it was like watching all his relatives argue during Thanksgiving dinner. At the end, the attitude was basically that everyone involved would just make it up as they went along. He and Spaihts knew that some movies would never work, so they joked that they might as well write the most oddball screenplay they could think of (such as including a character that would "kill [off] the monsters from the movies that didn't work"), because they felt there was no way the franchise would survive long enough to actually produce their film.

The film's tagline, "Welcome to a new world of gods and monsters," is a quote from Bride of Frankenstein (1935), which was also produced by Universal and would have been the next installment in the Dark Universe franchise if "The Mummy (2017)" caught on.