She was portrayed by Ally Sheedy.
In "An Evening With Mr. Yang", Mr. Yang makes her first appearance, to play her game with Shawn Spencer. After Henry's adamant protests to the contrary, Shawn accepts her proposition, vowing to bring her to justice. She first kidnapped Shawn and Gus' waitress and held her hostage. After leaving several cryptic clues for Shawn, the hostage was finally returned, but replaced with Shawn's mother, Madeline Spencer. After strapping a bomb to Madeline, Yang sat and watched as the SBPD swarmed a drive-in theater looking for her. Shawn found her car, and she finally came face-to-face with her target. She revealed to Shawn that she was going to write a book about them, and was finally arrested. <p class="MsoNormal">When Shawn and Gus speak to Mary Lightly (a psychologist who helped bring Yang to justice) a year later, in "Mr. Yin Presents", he reveals that it would be impossible for Yang to work alone, and proposed that she was working with a Yin. He discerns this from Yang's book, entitled From Serial Dater to Serial Killer: How Murder Kept Me Skinny. Mary's theory proves to be true, and Shawn, Gus, and Mary proceed to visit Yang in her tiny cell at an asylum. While there, Yang admits to working with a Yin. She says, "If you think I'm sick, you ain't seen nothing yet." This proves to be true, as Yin (representing chaos) has no rules. Mr. Yin then goes on to kill Mary, and then play a "game" with Shawn. He kidnaps both Abigail and Juliet, then forces Shawn to choose which to save. In the end, both are saved. <p class="MsoNormal">Yang's story is concluded in "Yang 3 in 2D". It is revealed that Yin is her father, and while she often aided him, she never killed any of the victims herself. She never wanted to be a serial killer, and wanted a life of family and friendship much like Shawn's. In the end, her father becomes her first true victim. Yang tells Shawn she will remain in prison on account for all of the Yin/Yang murders, not knowing any other existence. <p class="MsoNormal">In "Psych: The Musical", Yang is brought out of jail by the SBPD to help track down the escaped Z. She forces them to sing for her before she gives them information. While Lassiter, Juliet, Shawn and Gus are chasing Z, she escaped her guard and ran. She continued to Skype Shawn and help him with clues if he sang, until he finally tracked her down and accused her of killing Elisa, Z's love. Yang was upset that Shawn appeared to be losing his special gift, as this was untrue, but when Shawn was attacked by the real killer and hung from a rope, she attacked the man with a knife, driving him away and saving Shawn. However, during the scuffle she was stabbed, and she dies. As she dies, she sees her "angel", Mary, who implies she won't be getting into heaven, but he said he "knows a guy who knows a guy" and he'll try to get her in.