Nice theme, art, music, and gameplay! Really well made! :D This felt very reminiscent of Undertale's Undyne fight. As for improvements, perhaps some reasonable particle effects or screen animations would help make the game feel more intense. Also, I noticed that at one point the tentacles seemed to pop into existence (without any animation) and shoot a large volley of bullet, which felt a bit jarring since up to that point there was some anticipation in the animation. Overall, well done!