Brigid O'Reilly was a police detective in Manhattan, when she learned that Cloak and Dagger were attacking criminals in her precinct. At first she wanted to bring the pair to justice, but eventually she learned to trust the young crime-fighters.

Later, she took a squad of police officers to investigate a warehouse belonging to the same pharmaceutical company that was responsible for giving Cloak and Dagger their powers. Some corrupt policemen, led by Roger Falcone, exposed the other police officers to a gas to asphyxiate them. With her dying breath, Brigid swore vengeance on Falcone. As Brigid laid dying, Cloak and Dagger found her. Although they were too late to save the other police, Cloak surrounded her and Dagger with his darkness, while Dagger tried to revive her with her light. When this appeared unsuccessful, the pair abandoned her body to search for those responsible.

Though Brigid O'Reilly died, she was reborn as Mayhem. She helped Cloak and Dagger find and fight the corrupt police, and she killed Falcone as promised. She is now herself a vigilante, showing no mercy to the drug dealers and other criminals she pursues.

Brigid is being considered as a "potential recruit" for the Initiative program, according to Civil War: Battle Damage Report.

Powers and AbilitiesEdit

Powers

Mayhem exudes a green gas from her pores that constantly surrounds her. When others are exposed to the gas, it can create a paralyzing effect. O'Reilly often employs her claws in an effort to expedite the absorption of her gas by exposing her opponents' blood to the air. The gas can have hypnotic properties that O'Reilly uses to withdraw information from informants.

Mayhem is also capable of flight under her own power.

As Mayhem is technically dead, it may be possible that she cannot be killed.