Thanks for playing. Yes, I plan to adjust the difficult in the future, just wished I had it better balanced for the reviews, but it's a jam and these things happen.
The stamina bars on the character were the first idea, because they allow the player to look only at the character and the enemies, but came really late in development (like 4 hours before the end of the jam). Before that, the stamina bars were displayed at the sides of the screen, which was really not good.
Different enemies take different amounts of hits to kill. The triangles and squares take 2, the pentagons take 3. The plan was to give better feedback to the player when hitting and killing enemies, but this also wasn't completed in time, so this feature is missing.