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This was a movie I saw as a young child, which means it was probably made in the 80's or earlier, though conceivably it could have been early 90's. It was animated, but I don't recall if it was Japanese or Western.
The scene I remember most clearly is a young man coming to a house where an older man and woman live; I believe it was a son coming home to his parents. However, he now serves some sort of monstrous big-bad and has magical powers. I remember he made flowers grow out of his father's hair and one grow out of his nose. His mother brushes away the flowers from the hair but not the one on the nose.
Later, the big bad has some evil scheme going on that turns humans into these nondescript block people that look like they are crude stone carvings of people. They all start marching together, and you can tell that one of them is the boy's father because it still has a flower coming out of its nose.
I also remember a scene where the block people are climbing on each others' shoulders to make a big tower, and I think the main badguy is inside. The badguy himself is some sort of ghost or monster - I don't remember specifically, but I'm pretty sure he was non-human.
There might have been a unicorn as a major character in this story, but I may be confusing it with a different movie.
Does anyone know what show I'm talking about?