Kittelsen made many fantastic illustrations of characters based out of fairytales and legends. Images such as this and this one depict very nightmarish and haunting creatures lurking about. This image of humanoid creatures made from mounds of hay is especially disturbing.
Artist found thanks to BibliOdyssey's link to this gallery of Trolls. Check it out to see more work by Kittelsen.
I found this strange drawing of a giant skull face made from strange landscapes and buildings. It appears to be artwork for some band called "Sileni"?