This was done for a 300 Drawing Jam over at The Drawing Board.
I started with a pencil sketch which was then scanned into Photoshop. Further detail (mainly white linework over the pencils) was added for more interest. Then using a textured Photoshop brush with reduced opacity, colours were built up. Also tools such as the history brush, dodge, burn (using the same textured brush) and some noise at the end were used for added effect.
Great movie btw.