Ok so I saw this over 30 years ago, I was only a little kid at the time and I can only remember the barest of details.

It was an animated film, I think it tended more towards Japanese style of animation, more edges and sharper images. There was a scene where a boy/teenager was conducting music, but he was standing on a surface that appeared to be made out of ice or crystal and seemed to be making the music out of thin air and I think was using it somehow to try and stop or fight these collosal black centipede like creatures that were smashing up through the ice or crystals from below before burrowing back down into it as they advanced on him. I seem to remember them being insects, but can't rule out that they were giant spiky vines or roots.

The only other scene I remember is the boy approaching a block of ice/crystal and there's a small, black imp like creature frozen inside it. The boy seems sad and presses his hands and forehead against it like he's mourning or trying to thaw it out, but then somehow they switch and the boy is the one frozen and the imp is free.

That's literally all I can remember. One of my siblings who is older than me said they remember the movie as well, but are just as in the dark about it.