Nice work!! Love the concept here. Nice take on the prerequisite too. The idea of the water orb actually firing out part of itself really goes above and beyond in terms of the thought put into the 'HP is power' theme. Would be especially cool if your orb shrunk and grew depending on HP, so it really looks like its using parts of itself in attacks.
Pretty difficult! But intentionally so, I think!! :D :D (This game should be renamed 'Watch me run back to the water pool with 1/2 a HP and a slime on my tail') xD
Constructive feedback: Perhaps make the aim a little easier. You can only see the crosshair if you angle the camera down, and sometimes it seemed like my shots were missing when they seemed to be quite well aimed(?)
(P.S. Minecraft skeletons as placeholders- nice!) xD