To achieve that 'drawing' look I actually skip a step in my normal drawing process. I generally go through 3 stages, rough sketch, flushed out sketch, then polished drawing. For Ninja Sheep, I decided to forgo the polished drawing step and use the rough drawing as a template for my Adobe Illustrator work. The fly away line work makes for great detail.

 

The drawing that started it all. This was one of the first concept sketches for Ninja Sheep.