I like the concept of being able to buy anything in the game, it reminds me of how Baba is You turns the expectation of game rules on its head. I would like to see this expanded out to a few more rooms, because it doesn't get enough time to shine as a short demo.

It was not clear for some time that using different items while attacking was doing anything other than a standard attack, so some indication of that would be good (maybe swinging the item itself or a sound effect.).

I really like the idea of bending the tropes of the buying from a store. 

The art is really good, and I hope you save it for future use.

I think the core concept has some legs, closing it in a core game loop would make this a lot of fun.

Maybe some feedback on the fact that something happened would help with the guidance. I didn't realize I had used the door to steal his key until the second time I played it. The feedback could be as simple as a specific noise, particle effect, etc.

Overall, a great entry :D

I won!

I'm embarrassed to admit I ran around in circles a bunch because I didn't realize I won til I entered full screen on a whim. Solid entry, subtle commentary. Great job!