Cool game! It's very difficult though haha. Maybe have the projectiles/spawned-things despawn quickly in some regard. Unless you rush the boss and spam attacks the map feels like it becomes death. But it's still fun! I got to the third boss :)
btw you can fix "On the web version, I get this weird issue where fullscreening turns the screen gray" by making the game run in the background (in the resolution settings).