FDG Entertainment have just released a massive patch for Monster Boy and the Cursed Kingdom on Switch which finally adds multi saveslots.
Monster Boy 1.0.4 is expected to hit PS4 and Xbox One soon as well, and fixes over 100 bugs in the game based on reports sent in from the community.
Additionally, there are some balancing tweaks, along with a Flashing Light Reduction Option and a Haunted Manor map update which makes it easier for you to get through with point of interest markers on the mini map. Very cool!
Sounds like these address some of the major concerns with the game. Have you tried out the patch yet? Monster Boy and the Cursed Kingdom looks incredible and is now available on Switch, PS4, Xbox One, and PC.