I had fun making the Nintendo characters into characters from Japanese fairy tales such as:
Bowser/Oni (a demon),
Goomba (he's called "Kuribo" in Japanese because a developer kept telling Miyamoto that the character looked like a Kuri (chestnut), so I made him look even more like a chestnut),
Koopa/Kappa (Kappa is a demon with a weird haircut and water in the top of his head),
Mario is a woodsman, holding a Hammer Bros. hammer,
Mushroom retainers are fairly unchanged, same goes for the squid and the fish!
I also used something close to the same colour palette as Super Mario Bros.
Prints On Wood wrote an article about the show, read it here.
To see more artworks from the show, check out the Tumblr!