During her childhood, she was abused by her mother for being overweight, driving her to drugs and leading to her later fixation on becoming a mother herself. She became a drug dealer, which exposed her to situations that ultimately damaged her sanity; namely, being shot in the head by a police officer, and being put in Cloak's dark dimension. The origin of Shriek's powers is likewise unknown; she may be a mutant, or the powers may have emerged as a result of her time in Cloak's dimension.
During Carnage's violent escape from the Ravencroft Institute, he came across Shriek, who was also incarcerated and wished to join him. He freed her, and the pair embarked on a killing spree. They attracted the company of several other homicidal supervillains (Demogoblin, Doppelganger, and Carrion), and formed a "family," with Carnage and Shriek as the "parents" and the others as their "sons". Shriek also used her mental powers to increase the chaos by causing a number of New Yorkers to violently turn on one another, although the heroes were able to calm the people down before they did anything too serious, such as killing their own children. The killers fought a number of heroes, led by Spider-Man, but succumbed to in-fighting. Carnage slew the Doppelganger and left the others to their defeat and capture, although he was subsequently contained by the Avengers after a clash with Spider-Man, Venom and Black Cat.
Shriek was returned to Ravencroft Institute, and attempted to escape twice. Once, alongside the vigilante Mayhem and a handful of other inmates, she was defeated by Spider-Man and John Jameson before they managed to escape. The second time, she and Carrion escaped and tried to become a family. In the end, she absorbed the Carrion virus into herself to release her "son" from his suffering. She was returned to Ravencroft, where the virus was taken from her by the Jackal. After not being seen for a long time, she turned up in a background scene at the Bar with No Name. At the Bar with No Name several super-villains were betting on what was in a chrysalis recently formed. This chrysalis happened to be a homeless man nicknamed Freak after he had visited Doctor Curtis Connors laboratory and injected himself with one of Connor's experiments.
Sonic Beam: Shriek can generate sound waves, that she can utilize in the form of blasts, with which she can fly and damage her enemies. These sound waves can propagate in the dimension of Cloak, causing it great damage.
Dark Empathy: She can bring to light the dark side in people. During Maximum Carnage, she used this power to cause the city to go mad, causing, for example, that a woman would like to kill her children, or a man raping a girl, and acts of anger, vandalism, and general mayhem. Her left-eye shines with she uses this power.
Telekinesis: She is capable of psionically levitating objects and people.