Thank you so much for such a detailed review!
The blue sphere next to the health bar is accumulated water essence. It slightly increases damage, but we didn't have time to balance it properly.
As for the bugs (especially with the second boss), we overlooked them, and we're really sorry about that. We just ran out of time to polish everything. Regarding the first boss dying in the second phase, I was actually aware of it but couldn't fix it in time. I couldn't properly track down why it was happening; since the damage didn't increase at all, I thought it might just be a nice bonus for the player.
The idea of restoring flasks on kills is great! I initially considered adding small fountains before the bosses to restore flasks and health, but I decided that would make the game too easy due to the small map size. I've also already figured out how to fix the jump mechanics.
After the jam, we plan to polish the game and fix all the remaining bugs and flaws.
Thanks again for playing!