I really wanted to write about how terrible this movie was, however, after some time to process the plot, various tropes, and the general idea behind the Black Demon, it's really just an average B-movie with questionable ideas. There's no escaping the fact that suspending common sense or reality is an absolute must before watching, but I guess Black Demon does what I think it's supposed to - provide cheap thrills and nothing more.
The other elements aimed at providing more depth to what is otherwise a tried and tested formula do nothing to enhance the story or the film overall except to offer a more convoluted way of arriving at the naturally expected conclusion; by the end, I didn't care for the tacked on the spiritual element or notions of capitalist/corporate greed. That said, I was more interested to see Narco's cast members on-screen again. It's a shame this film didn't really live up to their talent.
The problem I found with this movie is that it didn't do a good job of creating the menace or terror of being hunted by a "70-ton shark". To be fair, there are previous shark flicks that are far more fear-inducing films that do a great job of creating paranoia and isolation; 'Jaws', 'Open Water', and even 'The Shallows' are still a tough watch, irrespective of how many times I've watched these films.
Though it might be entertaining to watch for a younger audience, Black Demon doesn't really have any depth to carry its main story for 140 minutes. JP