When I want to make something look extra freaky, I just put eyes and mouths where they shouldn't be. It seems to work well.
This happy little monster existed before I'd learned line width variation techniques or started cell shading things, so I had to resort to a different method to give it depth. My solution was to have three different planes of depth to the good: Foreground, middleground, and background, each with its own palette (except for the eyes, which remained constant). It would take something truly gargantuation for me to resort to that method for coloring a character now.
Commentary added October 31, 2014