An American Tail: The Mystery of the Night Monster is the 4th and thus far final installment in the An American Tail franchise. This film was released on December 9, 1999 in Germany and July 25, 2000 in the US.
In it, Fievel Mousekewitz is plagued by nightmares after news spreads of a vicious Night Monster terrorizing Manhattan and kidnapping mice. Tanya, who now works for the Daily Nibbler Newspaper, is forced to take Fievel to work with her in an effort to alleviate his fears. On the way they meet Nellie Brie, a famous undercover reporter. Her boss, Reed Daley, is constantly at odds with her, and as a bit of a prank he assigns Fievel to be her assistant and artist, putting him to work drawing interpretations of the Night Monster. Needless to say this does nothing to calm his fears, and he ends up with more sleepless nights. However, as Nellie attempts to get to the bottom of the mystery, clues begin to point toward an eccentric French poodle who recently escaped her owner and has taken to telling fortunes in the street, Madame Mousey, as the main suspect behind the disappearances.
The direct-to-video film uses many of the same character designs from the previous film, as well as many of the same voice actors. Like the film preceding it, The Mystery of the Night Monster takes place back in New York, putting the canonicity of An American Tail: Fievel Goes West into question.
This film provides examples of:
- Award-Bait Song: "Who Will", featuring singer Susan Boyd (Nellie's voice actress) being The Cast Show Off, while the rest of the voice actors' singing ranges from fair to Narm.
- Aww, Look! They Really Do Love Each Other: Nellie Brie and Reed Daley end the 4th movie this way after having been at odds throughout the entire movie. This comes much to Tanya's dismay, who spent the movie crushing on Reed.
- Baby Carriage: Although the sequence itself turns out to be All Just a Dream.
- Belligerent Sexual Tension: Reed Daley and Nellie Brie.
- Butt-Monkey: Twitch, one of Madame Mousey's minions. He even gets all four of his legs dislocated during her Villain Song.
- Catapult Nightmare: Fievel wakes up from one at the beginning.
- Deranged Animation: Fievel's nightmare at the beginning includes being chased through a Disney Acid Sequence by a demonic cat with a mousetrap at the end of its tongue.
- Dream Sequence: Done a lot when Fievel keeps having nightmares.
- Extra! Extra! Read All About It!: Tony Toponi becomes a paperboy, though he really wants to be a reporter and when he becomes discouraged and his rant begins to show it. * in a flat monotone voice* "Hey, get your paper here, whoop-dee-do paper here..." When someone passes him by he yells "Fine! So stay ignorant!"
- Floating Advice Reminder: As Fievel cowers before the mechanical "night monster" he gets a vision of his mentor Nellie Brie's floating head, telling him it's alright to be afraid sometimes, but not to let the fear win.
- Impersonating an Officer: Nellie Brie does this while on an undercover report.
- Little Miss Snarker: Tanya, who is particularly displeased to have to bring Fievel to work with her.
- Minion Maracas: Madame Mousey does this to Fievel after he calls her a rat.
- Nightmare Retardant: Invoked in-universe when it's revealed what the 'monster' actually is.
- Nightmare Sequence: Fievel's nightmares in the fourth movie, which are inspired by the exaggerated news stories about the Manhattan Monster eating up helpless mice.
- Oh God, with the Verbing!: One of Madame Mousey's cat underlings talks like Jerry Lewis.
- Old-Timey Bathing Suit: The Mousekewitz's along with Tony wear these at the beach at the end.
- Pep-Talk Song: "Get the Facts", sung by Nellie Brie to help Fievel get over his fears.
- Psycho Poodle: The Big Bad is a miniature poodle named Madame Mousey, who despises rodents because she is often mistaken for one, and so plots to get rid of the Nice Mice by kidnapping them and giving them to the cats.
- Team Hand-Stack: Done at the end of the song "Who Will?" by Fievel, Nellie and Tony. Tiger joins in, but has to use his finger because he's so much bigger.
- They Do: Nellie Brie and Reed Daley.
- Villain Song: Creature De La Nuit, by Madame Mousey.