I need help finding a fantasy or adventure movie from the '80s or even '70s in which, after the hero defeats the villain (a sorcerer perhaps), the villain falls to the ground and rapidly ages in a second, his head turning into a skull, and then to dust.
It was a similar effect as in Indiana Jones and the Last Crusade, but that is not the movie.
In my movie the head turning into a skull was on the ground, and it took a big part of the screen on the left. There was some dust moving, to describe the fast flow of time or just simple dust because it was some desert or something. There was only a helmet or a similar item left on the ground at the end.
We were taken to the movie theater by teachers, so the movie was considered kid appropriate; only this scene was scary. I believe that it mentioned that an immortal sorcerer (or knight, king, someone with authority) sent the main hero on some quest, which eventually ended his immortality. So I am not totally sure that the hero actually defeated him in a fight; perhaps his completion of the quest simply led to the aforementioned death.
Edit: a post from another site where I asked the same question, from a guy from my country who watched same movies in theater (that is, those which were bought and translated in the '80s in SFRJ), he has different memories from this movie, but the same about this scene I mention, so please check if that does ring a bell to anyone. He wrote:
I remember I watched the movie where is some young man in the main role, and he went on an adventure with some older man... or he did it in the favor of that older man. Because something like... that another guy is too old and this younger goes instead of him. Now when... when this young man fulfills those tasks (or maybe it's just one or two) that is an older man suppose to doo - older man rapidly age falls to the ground went to the skeleton and at the end disintegrate into the dust! And of him just stay a helmet and armor. But it's not the death of the villain and not death at end of the movie... it happens somewhere in the middle of the movie I think.