Ah, horror fantasy! You’re saying that we can mix and combine genres!

Hmm, are there rules to these combinations? Or can you just mix any of them together both willy and nilly?

Could you combine, say, vampires from the “horror” camp and ill-fated relationships from team “romance” like some literal, literary Romeo & Juliet? Would that not be a “Twilight”? Or would that be more “romance” than “horror”?