I've been pondering this and will go out on a limb and suggest Necessary Evils. I know it has virtually no connection to Korval but it is self contained and would make a great suspense horror movie. All the elements for a good suspensefull horror is there and some special effects visuals thrown in. The twist at the end is... positively chilling.

Of course I have no media expertise, but a good screenwriter could really play with this and shape it into a good movie along the lines of The Others or Angel Heart. That kind of stuff. In general, I don't like horror movies, especially slasher and zombie stuff, but this kind, I love.