Alright, so I've got some more comments:
3. Just figured out how to pass the part in the tutorial, that I mentioned I was stuck at. Apparently I have to sneak while falling. That's alright, and apparently there are tips for that, but I don't understand what they say.
4. More sounds, more indications! I don't understand how losing health works, because I was missing the moment when the health gauge was dropping. Also, I couldn't tell if I was hitting the boss, until he disappeared.
It's cool there's different music between levels, somehow I didn't see that in that many games recently.
5. The best way to avoid the skeletons for me, was to jump on top of their heads and carry me. I don't think that was intended.
6. It would be good, if throwing shurikens remembered the last direction it was thrown. It's annoying to keep pressing the direction button for that.