Parrying being your only or main source of damaging the boss is an interesting mechanic and a good take on the limitation. As for feedback, I'm not sure if it was intentional or not since it's a jam but it was entirely possible to sit in one spot and simple mash on parry whenever it became available. And occasionally heal. This, however, only worked for the first two bosses. I also think having more visual feedback for when you're doing damage (other than the lifebar) would go a long way for the actual "feel" of the game. A good bit of content though all things considered!