Trivia: Cesar Romero refused to shave his moustache for the role of Joker, so it's still visible under his makeup.
Trivia: The Grinch's face is partly based on Chuck Jones' own face. Jones said he tended to sneak his face in without even realizing it. (Source: NPR).
Trivia: Just after Linus seals his letter to the Great Pumpkin in an envelope, he walks past Lucy who is sitting on the floor watching TV. In her hands, Lucy is holding an issue of TV Guide Magazine. On the cover? Lucy, sitting on the floor in the same position, wearing the same blue dress. (00:07:00)
Trivia: Fred Gwynne (Herman Munster) and Al Lewis (Grandpa/Count Dracula) worked together previously on "Car 54, Where Are You?" This is referenced playfully after Herman and Grandpa discover the secret of Munster Hall.