Overworld ghosts and blocks

My Son Arthur, who is 6 1/2 is a big fan of Minecraft. His suggestion is that ghosts could be added to the game in the Overworld. When they are defeated they could drop into ghost blocks, or sub-items (ectoplasm?) which could be crafted into ghost blocks. He says he would like that a lot.  To add to this, the properties of the ghost blocks could be that they are translucent, had a glow effect and maybe even able to be walked through at night, or some other mechanic that made them non-solid (maybe even a controllable attribute?).

Thank you for your time and all our best.

Dad Jamie and Son Arthur