Overall, good job!
For the monster spit going through walls, I'm pretty sure they do that by default.
For the moving platform - I love this little feature you added yourself, but I would consider making it so by stepping on it, it goes all the way to the top (as opposed to the player having to stand on the button for it to go up) or perhaps making the button as wide as the platform. As it is, it's rather unpractical, considering the characters wide steps (even just turning around can make you leave the button) and the part with the monster shooting at you, where you can't really move to dodge.
For the difficulty - I would consider the scales on this one - yes it is frustrating, but it still has to be fun to get back, aka challenging. Here, the obstacles don't reset even if you die and some of the platforms do take a while to move. So in such case I would consider if it's still fun to get back up even if you fall or if it's just mostly going through already cleared obstacles and waiting. It's a hard thing to balance, but shortcuts or checkpoints can help.
Just to be clear, don't take this as a prompt to go back and redo this homework, you have already spent more than enough time on it and the resulting work is great! Take it more as food for thought for your future work :)