You got a lot more added in a short time than I thought you would, nice!
edit:
Bug report and idea time.
First, the bug. When fighting the boss I had something strange happen. I was one hit away from death and was in the middle of some aerial attacks when I got hit. Suddenly and very quickly, Arma just zipped into the wall and stood still. My health was gone but I was not dead for some reason. I couldn't move and the boss kept attacking the now immortal Arma. Had to restart the level to fix it.
Now the idea: Love the merchant but felt a little off that he was just standing there in the middle of nowhere with a stage infested by monsters. So I figured an introductory sequence would be decent. Simply put, you would find the merchant being harassed by the monsters and Arma would slay them. The merchant would then express his gratitude for the rescue by offering his wares at a discount (no actual discount needed).