Really nice game and concept! It was so fun and tricky, I loved it!
There is one issue with the Mac build, it is not marked as an executable so it can't be played. You can solve it by right clicking in the app, tap "show package contents", then go to Contents/MacOS and execute "chmod +x ./Possession". That makes it an executable and you are able to play.
Despite that, it was so nice, really good work!