Although originally aired in October 1997, this episode follows the events of the direct-to-video animated film Batman & Mr. Freeze: SubZero (1997), whose release was delayed after the poor reception of the live-action Batman & Robin (1997). "SubZero", a continuation of the previous Batman: The Animated Series (1992), was originally set for release in July 1997, which would have predated the fall debut of the revamped and redesigned series, "The New Batman Adventures".
Mr. Freeze's original character design for Batman: The Animated Series (1992) was done by comic book artist Mike Mignola, at the request of Bruce Timm. Like Mr. Freeze in this episode, Mignola's own comics feature at least two characters who exist as disembodied heads attached to robotic bodies: Herman von Klempt, a mad Nazi scientist whose head is kept in a glass jar, and The Amazing Screw-On Head (2005).
Mr. Freeze's next and final appearance in the DCAU is in Meltdown (1999), where his head is being kept in storage by Wayne-Powers. How this came about is not explained in the animated continuity, but Batman Adventures (Vol 2) #15 (based on the continuity) explains that the head was acquired by Derek Powers's father. Batgirl refers to how Nora Fries was revived, as seen at the end of the feature film Batman & Mr. Freeze: SubZero (1997).
After one of Freeze's henchwomen accidentally freezes her foot and is unable to move, Freeze doesn't help her and apathetically leaves her to her fate as he escapes. He showed this exact kind of treatment to his former henchman Johnny, who found himself in the same predicament in the Batman: The Animated Series (1992) episode Heart of Ice (1992).
The first appearance of Jack Ryder