Supernatural
Gothic novels emphasize horror, mystery and the supernatural. Three elements help embrace the characteristics of Gothic literature, atmosphere, action, and supernatural. Of those three elements I think the supernatural is the most effective, for so many reasons, especially in a novel such as Frankenstein. Without the supernatural a Gothic novel would lose its sense of danger that is very important when the reason of the writing is to invoke fear. It would also lose the magical aspect that keeps the reader interested. A novel such as Frankenstein thrives because of the supernatural aspect it contains. Without the supernatural Frankenstein would not have the monster, and not be considered scary which would change the genre completely.
