Murder Suicide: If Paul tried to grab for the gun, David will end up accidentally shooting him. Then he gets even more upset and shoots himself.
Freak Out: Had one in the past where he almost killed his mom. Remembering this some time later causes him to have another one and almost kill himself.
Extreme Doormat: Shirley accuses David of being this, saying that he wasn't kind, but insecure and that he didn't have a personality of his own. When David denies it, she leaves him.
Heroic BSOD: Suffers one when faced with an image of his mother and recalling some very painful memories.
Laser-Guided Amnesia: After Paul saves him from the Crooked Man compelling him to shoot himself, David doesn't seem to have any memory of the incident, is confused that Paul was beating up on him and insists that he was perfectly normal the whole time.
Mommy Issues: One of the big things looming over his life and keeping him depressed is that his mother has a tumor in her brain and can't even recognize him, and one time her upset over thinking he was a stranger invading her home was so bad that she had a Freak Out, leading to him also having a Freak Out and almost killing her. Remembering that incident in particular is what causes his Heroic BSOD.
My God, What Have I Done?: After he freaks out and nearly kills his insane mother. This particular memory is so traumatic that remembering it some time later causes him to go into a Heroic BSOD.
Nice Guy: A very important character trait. David's kind personality allows him to bond with Sissi (who lampshades it), D and Fluffy, but the Crooked Man also takes advantage of it. A book specifically says that "they" (spirits, the Crooked Man) would take advantage of people's kindness to manipulate them.
Sanity Slippage: His friends suggested he move for a change of pace and are shown to be very worried about him, and even his ex-fiancee calls him to check up on him. He had a Freak Out when his mom had a particularly bad breakdown and almost strangled her sometime in the past. Remembering this incident later leaves him so upset that the Crooked Man is able to possess him and almost compels him to suicide.
The Southpaw: In the times we see him holding something in his hands, like the lighter at the hotel and the gun when he is being possessed by the Crooked Man, David is holding it in his left hand.
Big Damn Heroes: He goes all the way to an abandoned hospital, runs up several flights of stairs, and punches David in order to save David when it seems he's being manipulated into shooting himself.
Cassandra Truth: Dialogue late in the game hints (and his character profile confirms) that Paul's always been able to see or at least "feel" supernatural things, and David and Marion had never believed him about it, leading to David being surprised when Paul believes him about the monster.
Chekhov's Hobby: Early on David makes an offhand remark about how Paul's into occult things. Paul can see dead people, hence him being able to follow the advice of Sissi, D, and Fluffy, and ultimately saving David from one of the Crooked Man's nastiest attacks on him yet.
I See Dead People: When he and Marion go to the abandoned hospital to find David, he can see Sissi, Fluffy and D, while Marion cannot. Later he briefly sees the Crooked Man himself, with one arm around David and the other holding David's hand with the gun up to David's head. After he saves David, David is surprised Paul believes him about the Crooked Man.
I See Them Too: In fact he's been able to see weird things far longer than David has.
A young woman David meets when he investigates an abandoned hotel. She is looking for something precious that was given to her by her boyfriend before he left her. Is really a "facet" of Duke's memory.
Damsel in Distress: David has to save her twice; once when the floor cracks around her and traps her, and later on when she gets attacked by the Crooked Man.
Dead All Along: Is really a "fragment" of Duke's memory, and Duke is himself dead.
Heroic BSOD: Say the wrong thing to her near the end of her chapter. Watch her give up on her quest to keep fond memories alive and drop the precious box her boyfriend gave her.
Meaningful Name: She feels like she's a sissy for being unable to let go of her fond memories of her boyfriend. Her ex boyfriend also told her that all she has is kindness, implying she's a weak person.
A young man David encounters while investigating an old law school. D is wandering around the place because he has fond memories of it. Is really a "facet" of Duke's memory.
Fiery Redhead: Has red hair, and the determination and slightly bad temper to match.
Freak Out: Has one when he learns a professor he greatly respected did not have high hopes for him at all and secretly mocked him behind his back. If you say the wrong thing when trying to calm him down, he stabs you.
Heroic BSOD: After he learns the truth about the professor he held in high regard. Say the wrong thing to him here and not only won't he come out of it, he'll freak out and stab you.
Only Known by Their Nickname: Is called "D" for "Dreamer" because he has such big dreams. A professor he looked up to secretly thinks it should be "D" as in "the only grade he'll ever get."
Tragic Dream: His dream of passing the bar exam. He's tried so hard for it, but has always failed, to the point that a man he looked up to and trusted secretly detested him for his inability to make it behind his back.
A little boy David finds in an abandoned hospital. Fluffy is waiting for his mother. She never comes. Fluffy too is a "facet" of Duke's memory.
Cheerful Child: At first, when you'll find him singing. But as things progress, he starts losing his cheer.
Curious as a Monkey: When accompaining David, he'll often make comments or ask questions about the objects you're analyzing.
Heroic BSOD: Gives up and leaves very upset when he realizes his mother is never coming for him.
Only Known by Their Nickname: He's called "Fluffy" because his hair is all fluffy! Do we know his real name, unless that's his real name after all? No.
Tagalong Kid: While Sissi and D are following their own missions, Fluffy instead follows David around.
Trying Not to Cry: He tries a (pretty flimsy) facade of bravery but ends up breaking down after he sees the Crooked Man for the first time. He then reveals he does this because his mom hates when he cries.
The Crooked Man/ Duke MacGahan
Starts following David everywhere on David's journey, and every time tries to kill him. It turns out he's the tenant David's been looking for this whole time. The reason he stalks David is because he hates David for being so much like him and wants him to die for it...and because some part of him wants David to not go down the same path he did and end up like him.
Driven to Suicide: He hanged himself sometime back, which is why he has such a nasty crick in his neck.
Implacable Man: David shoves him into a pit? Sets him on fire? Knifes him? Locks him in a room? Beats him with an iron pipe? Hits him with a fire extinguisher? Shoots him a lot? Nope. Not gonna stop the Crooked Man. Except the shooting. Eventually.
Literal Split Personality: Sissi, D, and Fluffy are all aspects of Duke himself. Sissi seems to be his regret over lost love, D seems to be his regret over his failure to achieve his dreams, and Fluffy seems to be his feelings of abandonment. And the Crooked Man is all his anger and resentment over all of that.
Mommy Issues: It's implied he's having abandonment issues concerning his mother; Fluffy, who is a facet of Duke, is found waiting forever for his mother who never shows up, and the Crooked Man is found dwelling in his mother's abandoned house.
The Resenter: Half of him really resents David because David reminds him too much of himself.
Stealth Mentor: While part of him genuinely wants David dead, at the same time part of him really wants David to succeed and is trying to give him the motivation to fix his life.
Sink or Swim Mentor: The situations he keeps drawing David into are all situations where David has to buck up or die.
Taking You with Me: It's possible that he wanted to drive David to commit suicide because he didn't want to suffer alone.
Unfinished Business: His attacks on David turn out to be him trying to come to terms with his own failures in life.
Was Once a Man: Before hanging himself and becoming a vengeful spirit.
You Are What You Hate: His reasons for trying to kill David; David reminds him too much of himself. And if Sissi, D or Fluffy are around he's more likely to attack them than David, since they are literally the aspects of himself he hates the most.