Trivia: Original "Hellboy" film series director Guillermo del Toro tried for nearly ten years to get a third film made in the series. However, due to a variety of circumstances, including budgetary concerns, his original vision for the third film was unable to be made. This movie was then written by series creator Mike Mignola and writer Andrew Crosby, with the intention of following on from the first two films. However, del Toro and original star Ron Perlman declined to be involved, feeling they should not make the film as it wouldn't pay off the storylines set up by the first two movies. Mignola and the producers then decided that rather than trying to make a direct sequel to the first two films without del Toro and Perlman, it should be rewritten to be a stand-alone reboot. References to the other films (and certain characters like Abe Sapien and Liz Sherman) were removed, and replaced with new concepts to set it apart from what came before.
Trivia: Doug Jones, who played Abe Sapien in the prior Hellboy films, was offered a chance to do a cameo but was unable to due to scheduling conflicts. A teaser at the end of the film suggests the discovery in a tank of a gill-man, possibly Abe Sapien for a potential sequel.
Trivia: Not quite clear perhaps to Hellboy fans or even to Arthurian legend scholars who watch this film, but Vivienne Nimue / the Blood Queen (played by Milla Jovovich) is meant to be the Lady of the Lake.