the original cartoon is used in the opening credits
Mentioned as a running gag between G and Sam.
George S. Irving's role as the narrator mentioned
Underdog was mentioned.
Underdog shirt seen
title character is correct response in "TV Cartoon Pooches" category
Joel: "There's no need to fear. Underman is here!"
Rooster mention the show.
Servo: "It's Underdog!"
Sergant Stimpy of the Klondike is a parody of Klondike Kat.
"Savior Faire is everywhere"
"Have no fear." Crow: "Underdog is here!"
A character in the film says, "Have no fear," and Joel adds, "Underdog is here!"
Joel: "Thank you, Shoeshine. You're humble and skeletal."
Referenced by Crow
Servo: "And the body of Chumley"
One of the balloons seen in the Thanksgiving parade is Underdog.
barbershop quartette performs the theme song
Fran mentions the series by name.
Servo: "Crow looks like Underdog, from the Macy's parade."
Monica mentions it.
Ross is asked who the voice of Underdog was during his grant review. Later he remembers it was Wally Cox.
Alluded to in title
Episode of the cartoon heard on a TV.
Mark is seen wearing an Underdog shirt.
A balloon of Underdog is seen during the Thanksgiving Day Parade scenes.
Much like Blue Beetle, Underdog takes an energy pill to acquire his super strength.
A clip of Underdog was shown.
Del can be heard watching it in the motel room.
Thunderdogg is a parody of Underdog.
everyone is amazed that Underdog can speak