That's a very nice concept! Well done =)

It's great to see someone implement a concept, which I personally only have seen once so far, which was the first boss in "Celeste". I think it fits well with the theme, but the death is way too punishing with it's long endurance and that loud scream.
Also you made the same mistake as I did with my own first platformer (I use unity too), which is that floaty feel when in mid air.
In a game where you have to be fast, you don't really want to wait a few seconds after a jump just to land on the next platform. As soon as I reach the next platform, the "impostor" is literally breathing down my neck and I have to try and get a gap between him and me again or die and restart the whole thing, which is very frustrating.

Not bad, turned out to be an interesting game :)

Fun game, I liked the concept, but I feel like death is too punishing and there should be a restart button (so I don't have to sit through the scream every time I die). The shadow is also maybe too close