Batman & Mr. Freeze: SubZero is a 1998 direct-to-video superhero animated feature film, the second based on Batman: The Animated Series, serving as a stand-alone sequel to Batman: Mask of the Phantasm. It won the Annie Award for Best Home Video Animation, and was produced by Warner Bros. Animation.
The film was delayed for a while due to the negative critical reaction to Batman & Robin, a live-action film that also featured Mr. Freeze as an antagonist. Nevertheless, SubZero received a strong positive response from critics, faring much better than Batman & Robin.
The movie is the second of a trilogy of animated movies based on Batman: The Animated Series, preceded by Batman: Mask of the Phantasm and followed by Batman: Mystery of the Batwoman. The film is directed by Boyd Kirkland.
Since his last encounter against Batman, Mr. Freeze has found a home in the Arctic and started a family (of sorts) with the still cryogenically-encased Nora, an Inuit boy named Koonak, and two pet polar bears, Hotchka and Shaka. Nora's condition begins to rapidly deteriorate due to a submarine accidentally emerging from underwater directly underneath them, shattering her containment vessel. Freeze returns to Gotham City with his companions. He enlists the help of Dr. Gregory Belson to find a cure. Belson determines that Nora needs an organ transplant, but due to her rare blood type there are no suitable donors available.
Freeze declares that they will use a live donor, even if it means the donor will die in the process. Belson is at first reluctant to kill an innocent girl, but Freeze bribes him with a gold nugget and even more gold from an entire vein in the Arctic that will put an end to Belson's financial problems. Barbara Gordon (Batgirl) is a perfect match, and Freeze learns from her roommate that she is at a restaurant with her boyfriend, Dick Grayson (Robin). Freeze attacks the restaurant and kidnaps Barbara, taking her to an abandoned oil rig where he and Belson are hiding. Freeze and Belson explain the situation to Barbara, who claims that she is willing to help Nora for the "blood transfusion", but not at the oil rig, prompting Freeze to keep Barbara imprisoned. When the time for the operation comes, Barbara realizes that they are lying when they say she will need to be put under for a mere transfusion. She escapes with the help of Koonak. Belson gives pursuit and almost catches her, before the arrival of Batman and Robin in the Batwing.
Freeze follows, and in the ensuing confrontation, Belson accidentally shoots one of the fuel tanks and starts a rapidly spreading fire as Freeze traps Batman and Robin. Freeze insists that Belson perform the operation, despite the oil rig blazing and ready to explode, but Belson betrays Freeze and attempts to escape, only to be killed by falling wreckage. Batman and Robin escape just as Freeze's leg is broken, but he tells Batman to save Nora and Kunac first, along with Barbara. Nora, Kunac and Barbara are put safely aboard the waiting Batwing with Robin at the controls, but when Batman tries to save the weakened Freeze, the platform collapses beneath them. Batman manages to catch Freeze with a rope, but falling debris knocks Freeze loose and Batman can only watch as Freeze is sent plummeting into the ocean below.
Batman manages to get back to the Batwing, and they fly away just before the oil rig finally explodes, but Freeze survives his fall and escapes just in time, and is able to hold onto Hotchka and Shaka as they swim to shore. Freeze returns with his polar bears to the Arctic to resume his life alone, having frozen his leg in an ice cast. He sees on a television in a research station that Nora has been revived after an organ transplant operation funded by Wayne Enterprises, moving him to tears of joy. Then he walks away, limping with a wooden stick for support, with his two polar bears as the screen fades.