Good start you've got here.

Movement felt pretty good overall. I liked randomly sliding around as I was exploring (so much so that I ended up getting permastuck in a one-tile high gap when I wasn't paying close attention XD). Upgrades made sense straight away for the most part. I wasn't immediately sure what the "devil cubes" were for the combo ability, to the point I ended up damage boosting through them instead of destroying them (though I worked it out on the way back... perhaps making these graphically different from background tiles might help). I had a bit of difficulty with the combat against the boars, feeling that their speed and the character attack distance didn't quite mesh well, but it wasn't too much of a problem once I thought to just jump over them and continue on my way.

Overall, game plays pretty well and the progression flow is straightforward to get through the adventure.

Hints: these items can be obtained in order: boots, sword, key, gloves and umbrella. You can reach the goal without umbrella, but I recommend all items collected, which means true ending of the game.