This episode has the first appearance of Nightwing. Dick Grayson, the first Robin, later uses this identity to become a hero in his own right in the pages of "Tales of the Teen Titans" #44. The creative team wanted to use Nightwing to subtly clear up the "Who's Robin" controversy and let viewers know that this Robin is in fact Dick Grayson and that this series takes place in the same universe as The Batman (2004).
When Raven is cleansed of her father's evil she wears a white cloak, just as the future Raven does in this episode.
The two people who throw snowballs at Beast Boy are modeled after members of the mutant gang from Frank Miller's "The Dark Knight Returns".
The original working title for this episode was "Best Friends Forever". However, the title was changed to "How Long Is Forever?" - which is a reference to a story by sci-fi author Philip K. Dick.
Warp is a villain from the comic book series. He is a member of the Brotherhood of Evil, a group of international terrorists. He first appeared in "The New Teen Titans" (vol. 1) #14. The French villain is able to create dimensional warps from one place to another. However, he is not a time traveler, as he is in this series.