This was very well done, great little game! I was confused by the upgrade system at first, but it made sense eventually. The movement was nice, unfortunately it felt like the dash was not really useful. The arena was just an empty box so nothing really to dash to/from. I thought the boss's attacks were really well done, different and interesting at each level. The hitbox of the attack was pretty small, either that or the boss hurtbox was too small - there were many times where the sword sprite was hitting the boss but no damage would register, that felt pretty unfair.