Thanks for playing! The difficulty does go up quite a bit in the later half, and the "mid-boss", while indeed intended to be a mid-boss originally, actually got promoted to boss status because I wasn't able to finish making the actual one. There is certainly room of improvement for the game balance, and you did pretty well!
There's a second gimmick to the rewind: it also serves a purpose in scoring. When you trigger a rewind while fully charged, you get to carry your current score and combo count back to the past, and gain score from that section again. I did put this information on the store page, but ideally, this should really be explained in an in-game tutorial (that I didn't have the time to make).
Reading this have made me aware that there's an accessibility problem inherent in the mechanic, though. Scoring isn't really useful when one is struggling to survive, and indeed the mechanic provides no advantage over a life stock for survival. There is definitely more to think about it later. Thank you very much for the feedback!
I'll surely post something on the implementation after LD!