A young girl with a skin condition that Sophie met at a mental institution. She died due to an experiment going awry, and her spirit had since latched itself onto Sophie.
- Adaptational Attractiveness: Zig-Zagged. While a freeze-frame bonus show's Diana's true form to be that of a nightmarish hag, the original short film's counterpart seemed to be an otherwise normal woman sporting a HELL of an Uncanny Valley Nightmare Face. It's up to the viewer which one is scarier.
- Adaptational Wimp: The fact that she can't exist in the light is the crux of the entire movie. In the original short film, however, this only seems to be the case, until the very last shot of the film reveals she has no weakness to the light whatsoever.
- All Take and No Give: Diana only exists in the physical world due to her parasitically feeding on Sophie. As such, their relationship is rocky at best with Diana benefiting from Sophie's misfortune, to abusive when Sophie's children come into the equation.
- Ax-Crazy: She inflicted a Psychic-Assisted Suicide on her father for shits and giggles, grievously wounded Sophie after hearing that she was to be released, and after her death and transformation, became little more than a feral beast maiming and slaughtering all in her path.
- Berserk Button: Trying to help Sophie with her illness immediately sets Diana off, and of course she reacts violently to the light.
- Big Bad: Of the film, and is slated to also be the main antagonist of the upcoming sequel despite Sophie committing suicide to save her two children from her.
- Can't Live Without You: After the experiment, Diana is tied to Sophie and can't exist if she isn't in the throes of her mental illness.
- Control Freak: She maintains an iron grip over Sophie's life, killing or driving away everyone else until it's only her and Sophie.
- Cop Killer: Killed the two police officers called to investigate a disturbance.
- Creepy Child: She caused her own father to kill himself from her mind games.
- Enfant Terrible: The experiment only turned Diana into a literal monster; as a child, she was already cruel and sadistic. She drove her father to commit suicide, became a Poisonous Friend to Sophie and eventually broke her legs.
- Evil Sounds Raspy: When she talks her voice is hissing and guttural. This is probably caused by the damage of the vocal chords caused by her exposure to bright light.
- Humanoid Abomination: Before her treatment, she was but a girl, albeit with Psychic Powers, an extreme weakness to sunlight, and a sick sense of humour, but afterwards, she became a disfigured, parasitic and deranged Living Shadow with murderous, bestial urges who anchors herself to the world of the living by fostering and feeding upon madness. Specifically, Sophies.
- It Can Think: Lures the two kids into a trap, and had written sadistic messages, taunting Rebecca that she was the one who murdered her father years ago.
- Living Shadow: Became this after her death.
- The Sociopath: She was an evil little girl, driving her father to suicide for amusement and established a manipulative, abusive friendship towards Sophie with no real love or affection, even breaking her legs out of simple possession when she heard that she was going to be released. After her transformation, shes become even worse. Her impulsive cruelty now extending to trying to kill Sophies children (despite not wanting anything to do with their mother at first) out of nothing more than paranoia and spite, and her Ax-Crazy tendencies amplified to the point that she goes on a killing rampage when pressed enough, tearing apart several people out of impotent frustration.
- Villainous Breakdown: Dashes at Sophie in a distressed, angry fashion when she was about to shoot herself.
- With Great Power Comes Great Insanity: Implied. Even though she was a definite head-case while human, when we see her later post-transformation shes now nothing more than a feral beast in both body and mind.
- Would Hurt a Child: At first, she seemed more fine with scaring Sophie's children, but it escalates to that point.
- Was Once a Man: Previously an anomalous but otherwise perfectly human little girl, now a warped, insane abomination.
- Yandere: For Sophie. After all, she needs her to survive.
The mother of Rebecca and Martin.
The main protagonist of the film. Sophie's daughter.