Oh! Thank you so much for playing my game! This is my first time making music, and I have zero knowledge of music theory (I can’t even play any instrument), so I only made a 15-second track... That's probably why it sounds a bit plain and repetitive... I'll keep learning about music production and work hard to improve this!
As for the difficulty level, I actually took inspiration from a popular little game in China called "Catch the Big Goose." The first few levels are just for getting familiar with the controls, and then the difficulty suddenly spikes in the final level... But looking back, it seems like I kind of messed it up—the last level ended up being way too hard... Maybe next time I'll adjust the difficulty better.