Possibly an more reliable way of doing a double layered D20 would be to have a setup like a magic 8 ball, so the inner die would float up to the view port up top. The overall die would need to be somewhat bigger and robust enough to be able to handle being rolled but i think i find that concept way more interesting than this double layered die. Something that’s about half the size of a magic 8 ball might work.
Also bonus: Magic 8 balls already use a D20 for the fortune thing inside.
