Deliberate mistake: When Hellboy is attacked by the spider-lady, as the spiders begin to descend on him to steal the sword, you can easily tell that some of the shots of the spiders coming down are repeated 2 or even 3 times, and simply flopped horizontally to appear different.
Hellboy Animated: Sword of Storms (2006)
1 deliberate mistake
Directed by: Tad Stones, Phil Weinstein
Starring: Ron Perlman, Selma Blair, Doug Jones, Peri Gilpin
Genres: Action, Adventure, Animated, Fantasy, Horror, Sci-fi
Continuity mistake: After Hellboy defeats the semi-vampiric heads, the Professor is seen destroying a small statue on his scroll representing them. Despite being destroyed, this statue reappears later in the movie.
Trivia: The concept of "Sword of Storms" having to do with Japanese mythology is actually based off an early concept Guillermo Del Toro had for the live-action "Hellboy" movie sequel. However, after plans changed and the idea was dropped, Mike Mignola (creator of the comics) and Tad Stones (co-director of the animated Hellboy features) decided this would be perfect for an animated feature. And so "Sword of Storms" was born.