One of the things I love about TV series such as Supernatural or Buffy is that they have their own mythology, their own way that monsters “work” within the confines of the setting. Movies do that too, but because they’re so focused on a single monster or a single premise, you rarely get to see it develop. There are exceptions, of course.
A demon in Supernatural works in a certain way, dies in a certain way. Likewise a vampire in Buffy. The audience is taught this, expects this, which – later, once this is established – allows the writer to mess with those expectations and create tension and drama in the process.
Steampower Publishing 