It's a little hard to see, but there are black platforms that you have to jump onto to get past the monsters. It's one of my very first gamejam projects, but I agree that this was executed poorly.
I just replay it knowing that and with brightness at 100% but still found it very difficult. If you remade it and change the brightness or made the platforms have a bigger contrast I think you would have a great game. I mean the art alone is great and the mechanics are fun and challenging but the small details are what break this game. If you ever fix those details I would love to play it