I've never seen "Cool World" but man this artwork is so rad. I can't find official word on who the artist behind this painting is but it could very well be Ian Miller, since he did other backgrounds for the movie.
My first job in games was concepting, modeling, and texturing lots of little characters on the same rig for a game called Raid Brigade, which I don't think ever left soft launch. I learned a ton though. The studio cited Funkos as their inspiration but with more facial features.