A free, unofficial ROM hack has just been released for the original Super Mario Bros. that transforms the classic Nintendo Entertainment System game into an entirely new platformer based on Studio Ghibli's 1988 animated feature My Neighbor Totoro.
Totoro - Mei is Missing (as the patch is called) features 14 brand-new levels inspired by the film as well as Ghibli's other works like Spirited Away and sees players take control of the furry forest guardian as they go looking for Mei, who has gone missing following the events of the original film.
As stated in the readme.txt, the creator Cakewarden started working on the patch a couple of years ago, with the original plan for it to be a simple character swap. However, they ended up taking things further than originally intended, creating a bunch of new levels, music, and enemies (based on characters like No Face, The Radish Spirit, Yubaba's Yu-Birds, and the Soot Sprites).
If you want to give it a go, you can download it now from either Romhacks.org or romhacking.net.