This is absolutely incredible. Every little detail contributes to a cohesive theme and they're so polished. I can't wait to dig into your source code and see how you put it all together. I had a blast playing it.
If I could make one suggestion, it'd be to draw more attention to the mode change when the countdown timer kicks in. Perhaps the music could escalate like a Mario game would when the timer gets low. Also, several times I was playing it with the sound down and I didn't notice the countdown timer in the top right. That could be me being tired or maybe there could be something else visually when the tension is ratcheted up.
This is amazing, dude. I've played it so many times already and will share this as much as I can. Well done!