I am a huge fan of adventure time and Bobby Chiu did this awesome fan piece!
Here is his process which is really inspiring to watch. I love how he almost sculpts the piece to what it is and how he just splashes on color making it all somehow come together. (If you aren't up for a 'life' pep talk just mute it.)
He also has a lot of other free demos! Check them out and let us know if you find any really good ones!