This one was a little rough for me. Things I wanna start with though: I think you did pretty well with the art. Everything stands out (save for some dark platforms that were hard to see to get to the castle) Really cool that you got a saving system in there, that's a big plus. While the music loop is a little short I think it works well enough for the game and I think it's pretty nice. I really like the idea of enemies having abnormal big parts as a take on the theme, I saw some rats with bigger arms and found them rather amusing. I think there's a cool concept here, but I am unfortunately getting capped by the combat.
Combat is a little rough. Your attack is slow and your enemies attacks are faster. Starting with the first boss, The Beast, it took me a second to realize what I was supposed to do. And even then, the windows to attack are so tight because of the slowness of combat while the beast is fairly fast and hits really hard compared to you that it's a bit much. I'd miss my window, be locked in a slow animation and recovery, while the Beast quickly snaps around and starts wailing on me as i struggle to get some distance again. But, I managed. Got the dash and was ready to face what challenges were ahead... Until I hit the castle. I think there are way too many enemies in there. With how combat feels to me, I don't feel like I can comfortably keep up with the sheer volume of enemies that I need to fight through just to make it to my next destination, since as far as I could tell, the castle was the only place I could go to after The Beast. I think combat would feel a bit smoother if the players attacks were a little faster and snappier since there's sometimes a lot of enemies to get through and maybe even slow some of them down a little so that the player has the advantage speed wise since the player is ultimately going to have to fight everything, so giving them some advantage to help them feel more in control of the flow of combat could help it not feel overwhelming if they encounter a bigger group of enemies.
Anyways, those are my take aways and gripes. Honestly, good on ya though. Making a game ain't easy and I think you still did pretty well with what you got, even if it's a little on the hard side. I hope I haven't come across too harsh in my feedback. Great work.