The Zeta Project is a spin-off of Batman Beyond. The character can originally be seen in the the twentieth episode of the second season of Batman Beyond titled "Zeta", where the synthoid robot is shown with a wildly different design.
Zeta's redesign is first seen in "Countdown". It depicts the return of Zeta to Gotham, and the first appearance of his friend Rosalie Rowan.
From Batman's point of view, this is a sequel to "Zeta" and the third time he's met Bennett (after "Plague").
Ro's 9-1-1 call echoes a theory voiced by Two-Face in the Batman: The Animated Series episode "Almost Got 'Im" that Batman is actually a secret "special" officer of the GPD.
When Ro is confronted by the Jokerz and addresses them as "clowns", the Top Hat Joker says "Not clowns. Jokerz". This is very similar to what was said by the original Joker in the Superman: The Animated Series episode "World's Finest, Part I".