This is a regression from the early DFTFU days, which
had transparent ghosts and wraiths (minus the emissive glowing eyes) before switching material workflow in Unity 5.x. I've not gotten around to fixing this properly yet, so this bug report should serve to remind me later. They will need some shader work to pull off correctly.
In the meantime, you should check out Pango's
Charcoal Ghosts mod. He overcomes the current technical issue and they look really great, much better than transparency alone could achieve.