I do a line drawing of simple shapes with a fine rolling writer pen or other hard ball-point. I press hard into the surface of rag board; it's a scrap from my mat cutting. Next I rub over the surface of the drawing with oil pastel. Finally, I load a brush with watercolor and flow it into the pen grooves which are free from the oil pastel. That gives us the batik/resist quality to the line.
This measures about 5 X 7 inches. I scanned it and use these mer-man 'tiles' in some of my unique collages- I'll post one soon.