Thank you so much for such a detailed and thoughtful review! It honestly means the world to me, and being compared to Undertale is a huge compliment that makes me incredibly happy.
As for the theme, my idea for "Spin to Win" was focused on the concept of circling and dodging around the bosses to survive. I thought that keeping yourself in constant orbit around them fit the theme well, though I can see how it might feel a bit loose in execution.
I'm really sorry that the second boss turned out to be too confusing! There are actually two hints hidden there, but I should have made them clearer. You can only damage the boss when his mouth is open-that's his only vulnerable state.
Thank you again for taking the time to share this feedback. I appreciate it more than you know, and I will definitely make sure to learn from this and make my future projects much more intuitive. Thanks for the rating! :D