Board Thread:General Discussion/@comment-36976813-20180921182734/@comment-28171460-20180928071744

Maybe I'm wrong, but I have the suspicion that the writer didn't read all the books that are being referenced in the film; he probably heard the name "The Headless Ghost", did some guessing, and created a Headless Horseman clone.

If my guess is true, it would certainly explain why so many of the monsters are just returning characters from the first film or generic horror characters (like the alien and horseman).