The Human Species Ch.20 - Farewell (Epilogue of Episode IV)
The spectreon exclaims, "a ghost!" "two, actually" the haunter sighs, "... or three. i don't have enough fingers to keep count anymore." "u-um..."
Evolution's Gate Ch.4 - Ghost's Story
"how about spectreon?" astrid suggests. "people, people... calm down" snivy says with a confident smile, "we all know this new eeveelution can have one name and one name only - poltergeon." they stare at him. "you know...
Evolution's Gate First Anniversary - Reader's Guide
Back on topic: apparently this spectreon is still able to die. it seems ghost-types are actually corporeal, if only some of the time.