Hi, just beaten the boss. The game is really fun! It reminds me of Downwell but upside down. I hope it will develop in the future!
I have two suggestions: 1. quick restart option (if you've taken a lot of damage at the beginning or don't like the items on the first stage), maybe make it so that it takes you to the first stage instead of the fireplace chamber? 2. Moving cursor over the item/knowledge gives their description (I had a few situations when I picked up an item in spikeroom or the room above the sideroom but I didn't manage to read what it does)
I also had a little bug. When I was in the sideroom and jumped on the enemy I was propelled into the ceiling and clipped through (possibly because I had the item, I think it's called promotion, that makes you jump of enemies realy high). I had no way to go back so I had to quit the game.