Batman and Harley Quinn

Harley uses Joker Gas on Nightwing to escape his interrogation. When Nightwing tracks her down at the Superbabes restaurant and pressures her to return to crime by helping track down Ivy and Floronic Man, she refuses. She asserts she wants a normal life and uses the gas as a desperate measure to prevent being dragged back into her criminal past, though it's described as a weak dose.

Poison Ivy uses her pheromones to mind-control Dr. Goldblum by kissing him every six hours. This allows her to force the kidnapped scientist to help with their plan to replicate Swamp Thing's plant transformation process. The pheromone kisses keep him compliant and under her complete control.

Woodrue kills Dr. Goldblum to prevent him from revealing any information that could help Batman and Nightwing track them. With the heroes closing in on their Blüdhaven location, Woodrue fatally wounds Goldblum to keep him quiet and eliminate the risk of him talking under interrogation or pressure.

Earlier, Batman questions Sarge Steel about the kidnapped scientist, establishing Goldblum as a key figure whose knowledge makes him a liability.

Batman defeats Floronic Man by setting him on fire. Harley points out that since Woodrue has become a plant hybrid, fire is his weakness. With Swamp Thing warning Woodrue that he won't intervene, Batman uses this to their advantage and sets Woodrue ablaze, destroying him and preventing the virus from spreading.

Poison Ivy stops her plan after Harley emotionally appeals to their friendship, using tears and personal pleading. Harley reminds Ivy of their past relationship and convinces her that wiping out humanity would also destroy everything Ivy loves about the natural world. This emotional appeal sways Ivy away from catastrophe.

Swamp Thing warns Woodrue that he will not interfere in the confrontation, though he hints at the peril looming over the Green. This non-interference is significant because Swamp Thing, despite being a plant entity, chooses not to stop Woodrue's villainous plan himself, allowing Batman to handle the situation instead.

Harley decides to help after bonding with Nightwing and learning the full scope of Ivy and Woodrue's plan. When Nightwing wakes up at her hideout, she shares her rejection letters and explains how her criminal past prevents her from being rehired as a psychiatrist. This vulnerable moment creates trust, and upon learning the virus would destroy all human life, she chooses to help stop it.

The scene at the diner establishes Harley's desire for a normal life, setting up her later decision to reject her criminal ties.

The Bio-Restorative Project is stolen S.T.A.R. Labs data that contains information about Swamp Thing's transformation process. Ivy and Floronic Man use this research to develop a virus that can turn every person on Earth into a plant hybrid, forcing humanity to 'go green' according to their environmental extremism.

They pursue Ivy and Floronic Man to Wainwright Swamp in Louisiana because Dr. Goldblum reveals, as he's dying, that this location contains the specific chemicals needed to complete the plant transformation process. The right combination of chemicals exists in that swamp to finalize their virus.

The pile of rejection letters shows that Harley has been trying to return to her career as a psychiatrist, but her criminal past as the Joker's associate prevents her from being rehired. This explains her desperation to leave her criminal life behind and pursue a normal existence, even working a minimum-wage job at a themed restaurant.

The Superbabes is a themed diner where waitresses dress as superheroes and villains. Harley works there while trying to go straight after her parole, though she questions why she's still wearing a skimpy costume for minimum wage. This setting reflects the film's crude humor and satirical tone.

In the post-credits scene, Harleen Quinzel reinvents herself as the host of a reality television game show called 'Ask Dr. Quinzel.' Contestants race through an elaborate obstacle course to win a year of professional therapy, blending Harley's psychology background with the film's comedic tone.