Mild spoilers—Joey learned how to hurt other ghosts by getting hit in the face with a saxophone
In game one, Joey says that ghosts don't normally feel pain, but he's "learned a few tricks". The first time we ever see him get hurt is in Blackwell Unbound, where he got hit in the face with a saxophone. So how'd he learn to hurt other ghosts? From getting beat up by Issac's sax.
Joey might have done something unforgivable when he was alive.
A few subtle hints are dropped in Convergence
that could indicate that, at some point during his life, Joey committed a terrible act. Possible spoilers are ahead.
- In Convergence, during the final confrontation with The Countess, at one point she points out that there's "something different" about Joey, that "everything about [him] is wrong". This may refer to the events of Unbound, but one should remember that, having had the door to infinity in her head wide open, The Countess can see pretty much everything. Perhaps, she sees something in Joey that neither Rosa nor the player are aware of.
- In Deception, we learn at one point that Joey had a past friend in late Danny Marconi, who is revealed to be the psychic Lisa Tenzin's grandfather. Earlier, at the Seagram Assisted Living center, Joey recognized an old man as Danny, who was able to see Joey because he was close to dying. The old man asked him "Why did you do it?", prompting a shocked reaction from Joey, who urges Rosa to leave the common room.