Nice idea, and really great graphics there. It took me a while to realize I could use the cores defensively (I kinda just held the left mouse button down the first few tries), but I then figured it out and killed the boss in about 4 tries. The only thing that felt off was player death. It was very sudden, and off-putting as a one hit game over. If time was no object here and you weren't under a deadline, I would like to have seen a life system at the cost of a harder boss.