Not sure if it's the Switch demo; wasn't even aware that was a thing. It seems to be the initial part of the game - the opening, a shipwreck, and then you can basically go as far as a little after the first boss.
The level up structure is basically out of the Adventure of Link, so when you get enough bones (souls), which you can also just find in the environment, you can level attack, defense, etc. If you die once, you lose your soul and you have to defeat whatever defeated you (or go back to the spot if the death was environmental) to get it back. If you die again, you lose all of your bones. Along the way you can find Bonestones that are effectively the souls you keep in your inventory, so you don't lose those, and you can pop them back at your lab to get more bones.
Regardless of the particular shape of it, I've grown tired of sprinkling something on top of failure/death, just as a little depraved treat.
Also, the way you restore lost HP is weird, where you have to maximize a yellow bar by hitting enemies and then you can use a potion to fill in the yellow bar. I didn't find it difficult to play around but it is bizarre.