A former psychiatrist who became a crazed criminal and Joker's accomplice and girlfriend, but has since broken up with him and become a solo vigilante. She is part of the Suicide Squad. Screenwriter Christina Hodson sought to reinvent Harley, wanting to expand on the character following her departure from the Joker. Hodson called Harley the character she enjoyed developing most due to her unpredictable personality.

A vigilante who is the orphaned daughter of mafia syndicate gangster, Franco Bertinelli. Ella Mika portrays a young Helena Bertinelli, during flashback scenes.

A vigilante with the metahuman ability of hypersonic screams, who is also a singer in a club that Sionis owns.

A Gotham City Police Detective (GCPD), who is building a case against Sionis.

A deranged serial killer and henchman of Sionis who carves a tally mark on his skin for each victim he claims.

A young girl who has a contract killing placed upon her head by Sionis, after she steals a valuable diamond from him.

Montoya's ex-girlfriend and a district attorney.

A brutal and iron-fisted crime lord who threatens Cassandra. McGregor described the character as "an absolute narcissist".