An old one but I still like it! :)
I had recently bought Ocarina of Time on the N64 and was really crazy about it. I first sketched it out in just pencil, including smudging to do the shadows I coloured it with colouring pencils and then went over the lines with a fine black pen. Finally I cut it all out and pasted it on plain white paper. I remember it took me around 5 hours on and off to finish!