On April 5, 2017, during principal production, Vincent Cassel and Mamoudou Athie joined the cast,[8] and the next day, John Gallagher Jr. was also added.[9] In May 2017, following the end of filming for the film, it was revealed that Gunner Wright was also part of the cast.[10] After shooting the film, the director decided to design the alpha creature based on H. P. Lovecraft's Cthulhu.[11]