I used to have nightmares about that dam swooping bird. I never seemed to be able to time it right and it used to swoop down and kill me almost everytime. I remember having to ask my older brother to do this screen for me everytime I came to it
The beanstalk was a nightmare for me as well and I too kept falling off it. The worst occasion this happened to me was when I had only 1 life left and I rolled off it. I had very nearly completed the game as well. I wasn't impressed, but I later came back to it and completed it a few weeks later.
The upside down world was tough to escape from for me I remember. It took me a good while to suss out what ledges to jump on to