That's a really high quality one for 30 days, very well done here.
Presentation is definitelly top notch here, and I played it on browser (since I wasn't able to download it for whatever reason) where you said it was missing some particle effects, so I really wonder how better it could still have looked.
The gameplay itself is also really good for the most part, and I specially love how you managed to make the entire map actually feel alive and interconnected, that was pretty neat.
I also think the 2 first bosses were pretty well made, but the final one felt really weird imo. It was noticeably rushed sadly, specially because of how simple and underwhelming it was, not to mention that you put a save station on the middle of it's arena wich made him super cheesable.
The level design was also really good for the big majority of it, but I need to admit, the right-most section of the map was a nightmare. not only it had pits of acid that were waaay too punishing to fall into, it's also the buggiest area on the game, so much so that it literally makes me take damage out of thin air and I have no idea why (I even recorded it to show it here)
I also suffered quite a lot fps drops on the bigger rooms and also on the final boss. This also happened with another Godot game I played, so for now I'll be blaming the engine for that, but still you should probably look this up.
Overall it's still a pretty impressive entry tho.