Harley Quinn appears as Joker's sidekick. The character actually originated on "Batman: The Animated Series," rather than in the comics.
The Joker wears a red helmet with yellow "Flash" bolts on the sides when he escapes on a rocket powered skateboard.
This episode was written by Paul Dini who is known for helping create Batman: The Animated Series (1992) and more specifically, the character of Harley Quinn.
The noted criminal psychologist Dr Eliott Blaine has the same mannerisms and speech patterns as noted expert on human behavior Dr. Phil.
As the opening credits finish, just as the scene shifts to the Joker preparing to watch TV you can hear the strains of Danny Elfman's Batman theme (also the theme to the Animated series)