Rendering is an easy process these days. But thinking about TRANSPARENCY opens a box of misunderstandings and options.
If you set a dancing character from opaque to transparent by giving him a transmission value of 1 in Arnold, he'll look like glass, and the shadows and reflections won't change. This puzzled me for a while, and here is how I solved it.
The music: "Computer Animation" and "Dubius 170", composed by me for this channel, licensed via GEMA.