It's an ambitious, aesthetically pleasing and charming little indie game, no doubt. However, it's still a bit clunky and (at least here) quite buggy.
I tried a couple of times to get past the supervisor. Sometimes he gets stuck at the right side of the screen (so you have to commit suicide to try again), when I finally beat him and got the letter, I saw no way to progress further (both sides of the screen were blocked, the boss is still playing his defence animation and the letter didn't disappear).
I hope it's not intentional (i.e. “you finished the demo” after two screens of gameplay). If it is, it should definitely end with a message telling you as such, perhaps with a link to your Steam page.
I would check the browser console here; it has a pretty long list of warnings with resources it failed to load.
Overall I wish the controls would be more responsive. This is most visible when you press 'Space' to defend, and still get hit because the animation didn't progress enough yet. I'd rather have the boss telegraph his attack, and then hit quickly (which you can also deflect quickly) – so you don't have to figure out at which part of the animation should you hit space.
Other notes:
– the leaf health bar is really creative
– I'm instinctively drawn to use the tip of the leaf as the cursor hotspot, but it's actually its top, which is a bit weird
– The resolution on Newgrounds is *massive*, so you have to zoom out quite a bit. How about a fullscreen mode? (Or perhaps you tried that, and it didn't let you in the way you do it:
“Failed to execute 'requestFullscreen' on 'Element': API can only be initiated by a user gesture.”)
– It's nice that you support a lot of languages
– The gameplay shown in the menu is a cool idea (but I think at one point you show the edge of the area with no background)
– The branch in the boss fight respawns in front of and dialogue and the letter text
– I think there should be an animation for jumping
– I wouldn't say dráb = supervisor; see https://en.wiktionary.org/wiki/dr%C3%A1b
Hodně štěstí. Zatím jsem vám dal wishlist. :)