Well, I saw the thread title and the first thing that came to mind was Casino Night Act 2. It took me months to figure that out. That was the worst introduction to a minor mechanic in a game ever, especially bad for such a simple game.
I had the opposite of that happen once, though. One day, long ago in like 1995, I was playing Commander Keen 4 with my sister. We were in a pyramid level and there were a bunch of inchworms following me on the ground. I said "hey, wouldn't it be cool if I connected these platforms so all the inchworms will come together around me, and maybe they'll turn into a gigantic foot and take me to the hidden level!"
And then they did turn into a gigantic foot and take me to the hidden level. On that day, I was a god.