Post History
In my opinion as a reader and writer I would say this. Write the level of gore you are comfortable with yourself but try to avoid long drawn out executions or needless violence unless it is require...
Answer
#3: Attribution notice added
Source: https://writers.stackexchange.com/a/27812 License name: CC BY-SA 3.0 License URL: https://creativecommons.org/licenses/by-sa/3.0/
#2: Initial revision
In my opinion as a reader and writer I would say this. Write the level of gore you are comfortable with yourself but try to avoid long drawn out executions or needless violence unless it is required to be in the plot. The mental illness should be based on real symptoms of the particular illness but no one person has all the markers and each individual is unique, so don't be afraid to perhaps tie it in to a multiple personality disorder. The "switch" you speak of seems to reference MPD perfectly. As for how much they can get away with is really up to you as the writer, I wouldn't want to see somebody get away with everything, there should be ups and downs in their success and failures I think it makes them more realistic. Lastly for how scary they should seem will be a natural progression of the gore and severity of the symptoms of the mental illness in my opinion. Best of luck.