Amazing Game ! The Art is great and the mechanics are easy to understand but hard to master. I loved the fact that we keep all the upgrades when we die. Little improvements you could do :
The first time i played the game i didn't see the first chest, the game where therefore too hard and above all my hp bar doesn't appear ! Maybe make it more obvious or force the player to open it (or maybe i'm just dumb)
Every time i die i have to fight the same enemies, and i have to loose a lot of time before making any progress. Maybe make the enemies disappear, or create new checkpoints. It would be great.
An inventory where you can see all your upgrades could be amazing (I know that's the kind of thing you don't have time in a Game Jam)
The Game was enjoyable and really atmospheric, i loved it ! Have a nice day !