Fact of the matter is that Arthur Fleck is a textbook case of Borderline Personality Disorder. These are the Mayo's Clinic list of BPD symptoms with my comments on Italics: An intense fear of abandonment, even going to extreme measures to avoid real or imagined separation or rejection.
1) Joker- Borderline Personality Disorder
However, the most prominent disorder he suffers from is Borderline Personality Disorder (BPD).
The psychopathology Arthur exhibits is unclear, preventing diagnosis of psychotic disorder or schizophrenia; the unusual combination of symptoms suggests a complex mix of features of certain personality traits, namely psychopathy and narcissism (he meets DSM-5 criteria for narcissistic personality disorder).
[Batman Forever's Riddler] appears to have borderline personality disorder, an unstable, incomplete identity characterized by chaos in one's thoughts, moods, actions, and self-concept...
Harley Quinn does not have BPD
Mainly in the comics, Harley Quinn is was seen to suffer from visions or fantasies, which could easily be interpreted as psychoses. This is not a trait of BPD but is actually a symptom most commonly associated with Schizophrenia or Schizotypal.
Maleficent, the evil lady from Sleeping Beauty is one of the evilest characters of Dinsey. She suffered from Borderline personality disorder (BPD) which means a person has inappropriate or extreme emotional reactions, is highly impulsive and has a history of unstable relationships.
In the "Titans" Dr. Leslie Thompkins diagnosed Bruce Wayne with borderline personality disorder.
Research indicates that BPD is linked to above-average intelligence (IQ > 130) and exceptional artistic talent (Carver, 1997). Because your partner with BPD may be exceptionally bright, they digest information and discover answers to problems more quickly than the average person.
Loki's dangerous antics and menacing lifestyle puts others at risk. Like Loki, persons with BPD experience disturbing emotional outbursts such as bouts of uncontrollable anger or rage--often followed by shame and guilt.
The problem with many of the BPD depictions we see on TV is that they fail to consider the totality of the character's lived experience. Instead, they offer an incomplete view of the person, usually through the lens of another character's fear and bewilderment.
For starters, Langley asserts that Batman, despite popular opinion, does not have a mental illness. The Dark Knight exhibits some symptoms of post-traumatic stress disorder, but not enough to warrant a formal diagnosis.
His psychological disorder was found in some scenes at the movie such as Schizophrenia Disorder there are 9 scenes and 5 dialogues, Trauma Disorder found in 5 dialogues, and Dissociative Disorder found in 1 scene and 4 dialogues. So, it can be concluded Arthur fleck has a mental illness.
Personality Disorder, specifically, Histrionic Personality Disorder plays a key part in Harley Quinn's life. People with Histrionic Personality Disorder are “pervasive and excessive emotionally and display attention-seeking behavior” (Bornstein 1998).
Stanlenheim and Von Knorring  suggested that borderline personality disorder was even closer to psychopathy than antisocial personality disorder, since APD is mainly limited to behavioral alterations, whereas BPD presents affective and interpersonal deficits in the same line as psychopathy.
David Haller / Legion appears in a self-titled TV series, portrayed by Dan Stevens. This version was diagnosed with schizophrenia instead of dissociative identity disorder and possesses psionic abilities such as telepathy and telekinesis.
Also, like individuals with ID, individuals with BPD also have neuropsychological deficits including lower verbal, performance, and full-scale IQ scores compared to controls .
One of the symptoms of borderline personality disorder listed in the DSM-5 is identity disturbance, where you have an unstable self-image or sense of self. People with borderline personality disorder have trouble understanding who they are or what their beliefs are.
We can definitely say that Loki is bisexual. This was revealed with his flirtatious comments towards Prodigy, his teammate in a comic series called „Young Avengers“. After this, it was confirmed that he had relationships in the past with both sexes in the Disney+ show Loki.
BPD is considered to be one of the most serious mental illnesses, as it causes a great deal of suffering and has a high-risk for suicide.”
Empathy and compassion – People with BPD experience greater internal and external turmoil. However, this in turn allows for the ability to recognise and have greater insight for others in similar situations.
Ability to sense the emotions of others.
Another gifting of BPD is a keen awareness of the emotions of others. Oftentimes a person with BPD will sense an emotion such as anger from someone else that the person is ignorant or in denial of feeling.
Borderline personality disorder is a mental illness often misunderstood by society. The associations made with BPD symptoms are scary and usually include self-injurious behavior, suicidal behavior, and extreme difficulty maintaining an interpersonal relationship.
The result of this research indicated that; (1) there are seven symptopms of antisocial disorder that occurred in joker character such as failure to conform to social norm, deceitfulness, impulsivity, irritability and aggressiveness, reckless disregard for safety of self or others, consistent irresponsibility, and lack ...
“Girl, Interrupted” is set in the 1960s and follows Susanna Kaysen (Winona Ryder), a woman diagnosed with borderline personality disorder during her stay in a psychiatric hospital following her suicide attempt.