You hover over the desk, pondering it.
It's difficult to truly touch things, but you try to focus and have your fingers press against rather than slide through the papers. Slowly, you push up on the edge of a book's cover and open it, looking at the marks inside. You can see the difference between the blocky repeated marks that seem like they're part of the page's pattern and the loopy irregular ones that were added later. You glance to the one in the bed, shivering too hard to do anything else, before returning to the book.
Did you have something like this? Did you sit in a chair, did the wood and gravity hold you like a hug? You don't remember anything like that, but they say that haunters are their ghosts, and they know so much else. If you could read this book like it could, would there be an explanation there? Did you have a life like this? Safe and easy and full of comfort?
Why do they get to have it and you don't?
It doesn't seem very fair. If you were once the same as all of them, maybe they should become the same as you.
Red/Green/FireRed: If you get the feeling of being watched in darkness when nobody is around, HAUNTER is there.
Blue: Because of its ability to slip through block walls, it is said to be from another dimension.
Yellow: By licking, it saps the victim's life. It causes shaking that won't stop until the victim's demise.
In terms of the pokedex's information, the original ghost-type pokemon line don't appear to be intended as the ghosts of someone else. They do appear amid graves originally, but that same location also contains a confirmed ghost who does not have the "ghost" typing. The closest is on gastly, very late in the series on Ultra Sun, as a "some people say" type of entry, and it's only from DPP on that any ghost pokemon start to have entries suggesting they're actual ghosts. However, the anime treats them as real ghosts, as do characters within the games.