An American Tail/WMG

Fievel takes after Papa.
It's very likely because Papa always has tells these stories, and Fievel's always the adventurous and curious type. And there's also the hat that Papa gives to Fievel at the beginning of the first movie.

Henri the pigeon was working with Warren and in charge of recruiting immigrants to work in his sweatshops.
Why else would Fievel be dropped off right at Warren's office instead of being dropped off at Immigration?
 * This makes America seem like even more of a Crapsack World when Fievel's betrayed by the one person who gave him hope in the first place.
 * If it wasn't Henri himself secretly working for Warren then maybe it was just the female pigeon he sent to take Fievel to Castle Garden.

Henri is a pimp.
Pretty self-explanatory. After all he's the only male living with a large group of female pigeons. Though for a pimp he's pretty good around kids.

Fievel Goes West took place after Treasure of Manhattan Island and Mystery of the Night Monster.
Fievel and Tanya look oldest in Fievel Goes West, and so it makes sense. Fievel saying that he dreamed he moved out west and became a famous gunslinger could be Foreshadowing. The only piece missing in this theory is Bridget being gone.

Warren is a size-changing shape-shifter.
How else can he be smaller than the rat who runs the sweatshop but as large as the other cats later on?

It must have something to do with that psychedelic mirror Fievel and Tiger sing "A Duo" in front of that temporarily made them the same size. That's the magic mirror Warren was using to aid his rat disguise.

Fievel's hat has supernatural properties.
It's like the One Ring; it has a mind of its own. At least it's protective of its wearer. It helped Fievel miraculously survive being swept overboard; and, in the end, Tony found his hat because the hat wanted to be found.

In Fievel goes West, it's able to morph into a cowboy hat because of its magical properties.


 * According to an old DOS game, Fievel's hat does have special properties.

Tanya has the voice of a siren and the power to tame any cat with her voice.
Just as Fievel has his supernatural hat, Tanya's voice has supernatural properties.
 * Which would, fittingly, explain its glass-shattering and hypnotic powers. So basically, she's Siryn?

Cat R. Waul was moving in on the Mott Street Maulers' turf in their absence because they weren't there to stop him this time

 * Waul might have tried his scheme of sending mice West to their doom before but had run into trouble with Warren's gang, who had an invested interest in the mice staying in New York. With Warren and the Mott Street Maulers gone, Waul saw his opportunity to edge in on Warren's former territory and take his mice away. Perhaps the two villains were former rivals.

Bridget and Tony are taking a break in their relationship during the 3rd and 4th movies, which take place before the 2nd one.

 * Maybe Bridget wanted to go back to Ireland for a time and fight for mouse civil rights there, coming back to America later and reuniting with Tony.

Bridget is still there in the 3rd and 4th movies, we just don't see her because she's at home with their new baby.

 * This is why Tony is so desperate to get rich in both movies; he needs a job to feed his family. And yes, this does imply he's swooning over Cholena while still with Bridget. Remember, this is a guy who fell completely in love with a girl after seeing her through the corner of his eye while walking by a knothole for two seconds! Not the kind of guy you could trust to be completely faithful, unfortunately.
 * In the third movie when Tony says that he has responsibilities now and he can't just go wherever he wants whenever he wants and Fievel gives him a knowing "Ohhh". That could be explained by this.
 * That could also explain why Tony was so freaked out in the fourth movie after the monster started grabbing everyone, maybe the monster took Bridget and the baby. The cats do say that the new mice are "Italian food" and after Tony hears them say that he tries to attack the cats without thinking it through.

The songs from the Fievel and Friends album are cut songs that didn't make it into the movies.

 * It should be noted that the first movie definitely did have one or two songs cut from it.
 * Apparently Jossed by one of the creators, Mark Ross, in the comments of this video. The songs were just made to promote Fievel Goes West, and weren't meant for the movies.

Cat R. Waul and Madame Mousey share the same owner.
They're both owned by a somewhat obese rich woman who likes to smother her pets to the point where her own pets hate her. She's The Faceless in Fievel Goes West, but we see her face in Mystery of the Night Monster, so they could very well be one and the same. Luckily for Madame Mousey we never see her owner put her through Marshmallow Hell like she does to Waul, but that doesn't mean it doesn't happen offscreen.

Treasure of Manhattan Island and Mystery of the Night Monster were All Just a Dream
After the events of Fievel Goes West, Fievel had a dream where he didn't move out west and he became both a mouse-rights activist for Native American mice and an artist for a newspaper. "Tanya: Ha! Like that could happen."

Mama and Papa hired a babysitter for Yasha during the second half of the first movie.
Sure the baby disappears for the second half, but would you really want to bring a baby aboard the Giant Mouse of Minsk, and then to search for Fievel through the city on the back of a cat, and finally flying on the back of a pigeon to see the Statue of Liberty?

Since in the AAT universe there's a mouse version of every human, it follows that there's a mouse version of you out there somewhere.
We all just have our Weirdness Censor turned up too high to notice them. Your mouse version, right now, is using a tiny laptop and browsing CheesyTropes.org (the mouse version of this site) as we speak.

Fievel Goes West is canonically the last movie because their baby daughter died.
Which is what prompted the Mousekewitzs' move out west. Too many bad memories in New York.
 * Pretty jossed, unless they had another baby and named it Yasha after the first one died, because she's in all the sequels.

Sniffles from Looney Tunes is a descendant of Fievel
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