Very polished and interesting idea ! I have to admit it took me a bit of time to realize I had to hover an item with the mouse before I could interact with it, I was trying to get close to it and press 'E' :D
I also had the feeling I was chasing after the ball at times, especially at then end of the fights when the enemy blocks are more sparse. Maybe having the ball rebound exactly in the direction of the mouse cursor would make its move more predictable and makes it easier to clear the enemy blocks ? or some kind of comb bonus where the ball gets faster each time it bounces on the knight