This was really cool lol. Presentation as a whole is on-point and definitely felt like a GBC game
The boss design as a whole was great, however death's scythe and projectile attacks were honestly impossible to dodge sometimes. I also felt that some attacks like the ice queen's blast attack when you take out her minions was a little cheap.
The hitboxes for some of these attacks were definitely a little too big, but I think the player really needed to either be somewhat faster, or have some sort of dodge or mobility move
The exchange mechanic is great though, having to use ranged attacks to get back health and use melee attacks to get back mana was really cool.
The normal jam difficulty was definitely a bit of a cake-walk, regardless of the weapon you choose ( Although I think the green weapons cheese the game somewhat ), but the harder difficulty was definitely more difficult lol
Loved how you re-mixed all the bosses, although it made some of the issues I pointed out above more noticable. I also feel like the rate at which health spawns in the harder difficulty was a little too low. And the amount of health you get back from collecting hearts was a little too low as well ( in the harder difficulty specifically )
But either way, it is a harder difficulty lol. I expected to get my butt kicked and I definitely did. I just feel like the game could have used some balancing and tweaking here and there.
None the less, you've made something absolutely amazing here. Great entry overall