The boss fight was too easy in my opinion. Once the smaller things were killed, you only had to circle around the field, aiming to not get hit and kill the smaller things
1 advice: go for the mysterious upgrade (the one costing 3000 stars); when going too low, it transforms you into a hedgehog'ish thing which bounces when you hit the ground, while still being able to use all the bonusses like gold star, windmill,...
 "Nightmare Runner"){kind=icon}
 "Mite Love"){kind=icon}
 "Flight"){kind=icon}