Key elements of the horror genre analysis

After analysing 'Rec' and 'The Ring', I have found that both films have a main protagonist that the film revolves around however 'Rec' has two main characters as it made to look as though it is filmed by one of the characters. However 'Rec' does not seem to have a antagonist as it is based on a disease but 'The Ring' does have a main antagonist in the form of Samara who is the person behind the killings. In 'The Ring' the antagonist seems to have a mysterious quality to it as it takes a while for the characters to find out who the antagonist is. Both films also have stock situations that make up a horror with a sudden realisation of who the antagonist is. Both films also have similar themes that are raised for example killing, and eerie situations that arise. The point of this exercise is to find out formulae's of horror films so that I can apply them to my movie trailer.