So here is the problem.
I have 1 layer with lots of objects with alpha textures and another layer with 1 solid object, positioned to appear somewhere in the middle of those alpha-textured. I have animated my camera to fly through the alpha-textured objects and copied it to both layers. Then tried to composite it in all the ways I found but it doesn't work. I think, the problem is that my layer with alpha-textured objects is treated like a whole by a compositor and as a whole it does not have any alpha, because there are so many objects that together they are overlapping till no visible transparency left. Alphaover, z-combine and 2 z-combine(with 1 inverted) don't work.
I'm trying to fly with camera and to see my shiny object through those alpha-textured objects. If I put it in the same layer it works perfectly but then I can't add effects to an object.