This was the first time Barbara Gordon's new identity, Oracle, appears in a Batman cartoon series. The character did, however, appear in live action on the short lived series, "Birds of Prey."
When Batman exits the Batmobile, revealing the 2027 Batsuit design, Mr Freeze remarks, 'the Dark Knight returns.' This is, of course, a reference to the Frank Miller graphic novel of the same name.
This episode takes place over a thousand years in the future, in the year 3027, with flashbacks to 2027. The Batman is drawn exactly as he was drawn in Frank Miller's graphic novel "The Dark Knight Returns" that takes place in the twilight of the Batman. Also the design of the future bat-mobile is taken from the Dark Knight as well.
Several times throughout the episode Robin is referred to as "Red Robin" In the comics Red Robin is the name taken by Tim Drake (3rd Robin) when he went independent after several years working alongside Batman
During one of the 2027 scenes when Nightwing saves the pilot, he glides away using wing like fabric beneath his arms. He has a strong resemblance to Batman Beyond(Terry McGinnis) which also takes place in the future where most of Gotham's heroes are old and retired