Screaming Mantis is one of four members of the Beauty and the Beast unit and controls all of the other members. She, like all of the other members, suffers from Post Traumatic Stress Disorder.
Screaming Mantis obtained her mantle in South America, stumbling into a torture chamber and ending up locked inside. Trapped with the victims for a period exceeding 10 days, she survived at first by drinking dirty water and later feeding upon the bodies of the male torture victims. Their screams drove her to insanity to the point that she hallucinated a black mantis was the one killing the males, unable to face the truth herself. To drown out the sounds of the screams in her head, she constantly screams herself, becoming the Screaming Mantis.
An unknown time later it was said that she was captured and given the personality of Psycho Mantis via nanobots and hypnosis in an attempt to control the other Beauty and the Beast Units so that they would actually be effective in combat. Psycho Mantis returning from the grave because of this was an unintended but much welcome side effect, him being able to partially manipulate the women into functioning as actual war machines. Because of her role as the internal leader and controller of the Beauty and the Beast Unit, Drebin calls her the "Beast of Beasts."
Screaming Mantis is perhaps the most powerful and intimidating member of the Beauty and the Beast Corps. Able to fly by some kind of unknown ability, she also seems to be able to manipulate the knives around her with this same ability. It's rather apparent that she has great mental abilities that allow her to crush people at will. Additionally, it seems as though she can take control of the minds of soldiers, manipulating them like puppets to do her bidding, including killing their former allies. Turning these men into marionettes seems to be a particular favorite of hers; in fact, dangling from the many arms of Mantis are two puppets that appear to be Psycho Mantis and The Sorrow from previous Metal Gear Solid games. It has been revealed that the Psycho Mantis puppet is used to control and manipulate living people while The Sorrow puppets can be used to manipulate dead bodies.