Sketchy Shadows is a feature of NprTools , which creates shadows using sketchy edges or Sketchy Patterns from your SketchUp drawing.
Here is an example of a model with Sketchy Edges, but normal SketchUp shadows, and the same model with Sketchy Shadows:
The Sketchy Shadows are created as a .JPG file and loaded into your .JPG viewer.
(If you don't select Launch when complete, you can find the final image in My Documents\NprTools\NprTools_Images)
You can adjust options like Line scale factor and Darkness to fine tune the final image. (See Settings below)