Iam gonna check for the sprites , as for the tilesets I have an advice for you. Instead of looking for"Horror" tilesets you should edit the RTP tilesets in photoshop/paint,It will look alot better. Here is an example,
I took this tileset
Changed the contrast and brightness so it turned into this:
Then I made a fog and it ended up like this:
So what Iam sayin is ALL tilesets can be made "Horror" like :P
Ps: Original
If you need any help editing tilesets and making fogs I'll be happy to help