Onyx is a character from DC Comics who has been both an enemy and ally of Batman. She appears in the DC animated film Batman: Bad Blood, working alongside fellow assassin Heretic. She does not speak and her background is not explained, but she appears to be deeply loyal to Heretic and helps him in both his mission to capture Batman, and later Batman's son and crime-fighting partner Robin.
After Heretic is killed by Talia al Ghul, his true master and creator, Onyx seemingly snaps. At the end of the film, as Talia is making her getaway in a small aircraft, Onyx appears from behind to attack her, hinting at the possibility that she perhaps loved Heretic and wanted to avenge him. As Onyx and Talia fight, the craft crashes and explodes, though it is unclear if either one of them died in the crash.