Let me start by saying a plague doctor game such as this is something I've wanted for a while and this project is amazing. I haven't finished the game yet, but there are some issues I'd like to point out.
Firstly, I understand that this game is supposed to be very hard (and it is), but the parry windows for basic enemies should really be a few frames longer. If I end up parrying too late, then I'm pretty much garunteed to get hit again by the next swing. I'm not entirely sure why I'll always get hit a second time and it's definitely at least partially my fault, but either way it feels too brutal for basic enemies at the start of the game (the boss and harder enemies can stay as they are).
To stick with the theme of difficulty, I just really wish there was a checkpoint before the traps. Yes, I'm bad at the game, but I think this would be a good change that still keeps the game really hard.
My other complaints are all very minor, and have to do with polishing. I'm sure you are aware of the incomplete inventory (the "heart piece" doesn't appear anywhere that I could find), and that the pause menu is still missing.
I can't stress enough that these complaints are hardly complaints, but I'm still going to point them out. I found myself wasting a syringe by bumping the f key after taking my left hand off and bumping it when I put my hand back on. A simple fix to this is to just make it so you have to hold in the button for a half second (kind of like focusing in Hollow Knight). You could also make it impossible to use at max health but that's not really neccesary.
Falling through ladders was also slightly annoying to me, I think following the traditional rule of pressing down to go through it at the top would work better. I'm realizing as I type this that you probably made it how it is because you'd want to parry while over a ladder. I'd still prefer to go through the platform, but I understand why it's like that now.
I noticed a few of the jumps including one in the tutorial require coyote jumping. I'm okay with that, but I think the coyote jump window should be a few frames longer so you don't get stuck on a jump so easily.
Thank you for taking the time to read this, I really do love the demo and I wish you the best of luck in the development of it.