This was super neat! I think I got to the fourth room or something like that and started feeling like "ohh this is interesting". Then when the big sword came along and suddenly you could "invert" enemies my brain literally exploded. Very cool, very enjoyed.
This is a thing of taste, but generally I really like when pixel based games maintain a constant pixel size, or if it's multiples of each other (like double the size or half the size). It just feels a little unsatisfying when the character steps on the text in the start and the pixels don't align.
On a different note, the puzzles are super super satisfying and really well paced, I never felt like I was babysitted or like I was completely lost. Those times where I had to go back felt quite fair, even though redoing the puzzle before was a bit frustrating and discouraged exploration. Everything was very predictible, which makes for a really good puzzle game.
Great work!