What are the karmic consequences of writing horror / fantasy fiction? Once I heard that Edgar Allan Poe is still being "haunted" by his creation, his Raven, because countless readers all over the world keep feeding energy to it, like a tulpa that never dies.
Many terrible things might happen from works of art/fiction, and they're quite unpredictable. 

I believe that the bad karma comes from how you react to the work of fiction, just like how one reacts to videogames, but still, I'd like to know if there's some obscure karmic concept concerning expressing the "evil parts of our soul / mindstream" through art.

For example, Dario Argento created some pretty horrible movies, but might be a nice person. Similarly, Chih-Hung Kuei directed a pretty horrible movie about Wu / chinese "Black Magick", but had some touching / beautiful buddhist principles on it.

Is it ok to write / create horror fiction if it has a "good ending"? Does it generate bad karma for having no "good ending" whatsoever? Is it terrible only when the creator feels "haunted" by it? (This last one seems quite obvious, but anyway). Does the fact of giving life for a terrible concept / idea / tulpa by itself generates bad karma upon the creator and/or the viewers/readers? Does a sad song generates bad karma on the composer if the listener commits suicide listening to it? etc etc etc.

What are your views concerning art creation and bad karma resulting from it? (Not considering profit out of the work of fiction, necessarily).
You reap what you sow. If your motivations was to frighten people Karmic consequence might be to be the author gets frightened also. If your motive is profit as expence of reader getting deluded, start craving, being lustful, being averse or frightened (aid the arising of the unwholesome roots) the expected karmic consequences may not be so good.

If your motivation is to send a constructive message then it might not be bad Karma after all. It might not be the ending that matters buy what motivates you to do it. 

Perhaps a book to teach Karmic consequence in the lower realms may not be a bad idea after all if you are thinking about writing. Khuddaka Nikāya's Petavatthu (and even perhaps Vimānavatthu) section may be a motivator for such stories.

Also the working of Karma is complex so it is not possible to give a definitive answer.