Ive been doing these for awhile now---at work, in between tasks I'll just doodle a little bit at a time. ..this particular one took me the better part of a week; one minute here, two minutes there, & it's finally done.
I might also add this is drawn on scrap-paper, with nothing but a pencil, eraser & two office ballpoint pens.. .maybe just cuz these supplies are readily available? Nah, it's because I can't afford Prismacolors yet