Good fun and original setting for a RPG! I'm a big fan of retro games so this game caught my attention immediately. Quite a few original ideas and plenty of humor too. Just a few nitpicks, mainly aesthetic:
* The green color used for the grass is really flashy, I understand it's probably from a specific GB palette, but toning it down a bit could make it overall more pleasing for the eye.
* The characters look a bit flat when shown from the side/profile, including the hero. They could probably do with a couple more pixels to make them look rounder.
* Some enemies sprites look much smaller than others (mushrooms compared to slimes, for instance). Scaling them all a bit could help.
* This is clearly a personal preference, and I understand it wasn't like this in old games and would probably require a lot of redesign for some maps, but I keep bumping in the top of trees when I expect to walk behind them xD. I guess I'm just too used for them to be displayed above the character.
Anyways, really nice game so far, keep up the great work!