Fake Russian: Fievel's voice actor wasn't even remotely Russian, and neither was Tanya's. And Papa's voice actor, Nehemiah Persoff, was born in Tel Aviv, Israel (then Palestine). Though he and Fievel's voice actor Phillip Glasser were Jewish, so they were halfway there.
On the other hand this is averted in the Latin American Spanish dubs, since he was voiced by male voice actors using a more younger voice.
Cut Song: Fievel was supposed to have another song in the sweatshop.
The Danza: It's quite possible that Fievel's nickname 'Philly' was chosen because of the name of his voice actor, Phillip Glasser.
Dueling Movies: An American Tail and The Great Mouse Detective. (Sort of; that movie came out in the summer, while Tail was released for the Thanksgiving/Christmas holiday season, though things were tense as Disney watched how well AAT would do in comparison to GMD.) An American Tail won and became the highest grossing animated film in history up to that point, but that isn't to say The Great Mouse Detective wasn't successful. Still, it's been said that this was the movie that gave Disney the kick in the pants it needed to improve its animated films.
Executive Meddling: This film and The Land Before Time were the only examples of this notbeing a bad thing for Bluth. Creatively, it was always Spielberg's word over his, which he was not happy about, but then again, it wasSteven Spielberg, although Bluth claims that Spielberg at least gave him the space to do his job properly. Both parties, however, were victim to Universal's lack of funding, as the higher-ups had no way of knowing whether or not it would be successful, resulting in several unfinished scenes and a somewhat choppy plot. Spielberg, who had never worked in animation before, was also frustrated by how notoriously slow and expensive it was to create even a single scene.
When David Kirschner came up with the idea for this, it was originally intended to be a half-hour television special, but thought it would be better as a full-length animated feature. He decided to turn to Disney, but the studio turned it down on the grounds that a story about a Jewish mouse was not commercial, leading to Kirschner relying on Steven Spielberg and Disney exile Don Bluth to make the magic happen. One wonders how much of an impact it would have made for pre-Little Mermaid Disney if they actually trusted the audience enough in not feeling alienated by the hero's religion!
The movie's plot was originally meant to be a flashback story told by 107-year-old Fievel to his great grandkids in present day. The reason the idea was scrapped idea was likely scrapped because it was felt really unnecessary. There's also the utter impossibility of a mouse becoming a centenarian (and even if Fievel aged like a human, he'd be close to the equivalent of one of the world's oldest; not impossible, but not very believable) note It does happen in the book adaptation, though. Also, one wonders if this idea was not ripped off in The Legend of the Titanic, also starting off with an old mouse recounting an event when he was young to his family.
Fievel's nickname "Philly" wasn't in the original script (and therefore, neither was the Chekhov's Gun of Tanya's name being changed to Tilly when the Mousekewitz's arrive in New York City- after all, "if it's not essential don't include it in the story".) The nickname was added because Bluth thought that "Fievel" sounded too foreign, and audiences wouldn't like it," so Spielberg and Bluth agreed to have him be called "Fievel" by his family, but "Philly" by everyone else. Bluth was ultimately proven wrong.
Jerry Goldsmith was considered to compose the score, but was too busy with other projects and was replaced by James Horner. Had things turned out differently, it would have been the second collaboration between Bluth and Goldsmith, after The Secret of NIMH.