I have recently found a writing prompt that I have started to develop into a short story/novella. It is a prompt that would typically be in the 'horror/thriller' genre; however as I've worked on it more; I noticed that I have formed a plot that mixes the genres of horror/thriller/ murder mystery. The basics of the plot is a teenage boy having just moved to a new town and house; and one night discovers a ghost in his cupboard- a blood covered 'tween' male ghost. As my plot develops, it reveals that the boy (ghost); was murdered; and it became a cold case; the boy (human); agrees to help the ghost discover his murderer. Is this mix of genres plausible; or have I just made the novella into a completely new genre? If so which genre? If not, is the mix of genres 'correct'?