Mercy Graves

Mercy Graves is a major antagonist in DC Comics. 
In Rebirth, she is the main antagonist the present day a storyline of Supergirl and Nightwing: World's Greatest (where the titular characters discover Conner) and major antagonist in the Supergirl and Arrow crossover, Crisis on Two Earths. After the run in with Nightwing and Supergirl, Mercy of Earth-9 was freed by Lillian Luthor and worked with her and other villains from the Green Arrow and Superman Rogue gallery in taking down Supergirl and the Green Arrow