Mrs. Norris' looming presence in the Harry Potter series is far too magical for her to be an ordinary cat, and there's enough evidence to support a theory that she's a Maledictus like Nagini. Filch's nosy cat appears all throughout the book series and occasionally in the films. In the movies, five separate Maine Coons play the intrusive creature. While Mrs. Norris' breed is technically never mentioned in the books, the Maine Coon is a specifically good choice given their intelligence, trainability, and social behaviors. Ultimately her role in both the films and its source material is to follow students around and report trouble back to Filch. While the cat isn't ever described as magical, her behavior definitely doesn't suggest that of a regular animal.
Described as having "bulging yellow, lamp-like eyes, a scrawny, skeletal body, and dust-colored fur," Mrs. Norris first appears in Harry Potter and the Sorcerer's Stone, helmed by director Christopher Columbus. Filch's cat is responsible for chasing Harry, Ron, and Hermione into the 3rd-floor corridor, which hides Fluffy and the Sorcerers Stone. She gives Harry constant trouble when he wanders the castle with his invisibility cloak. In Chamber of Secrets, she's the first to fall victim to the Basilisk, causing great stress in her owner. During Goblet of Fire, she almost gets Harry caught for going to the Prefects bathroom while trying to crack his golden egg clue. Truly, she's probably responsible for half the detentions that Filch gives out.
While Mrs. Norris gets a lot more attention in Rowling's Harry Potter book series, the cat maintains a strong presence in the films. Her aptitude for understanding when students are breaking rules and her almost telepathic synchronicity with her owner certainly leads to some raised eyebrows. It's clear from her behaviors that she's at least magical in some way. Perhaps her origin story is similar to Nagini's if she is, in fact, magical. There are a couple of reasons that this theory does hold water.
Mrs. Norris Shows Up On The Marauders Map
In Harry Potter and the Prisoner of Azkaban Harry, discovers the Marauders Map, a magical device that shows most of the school's secret passageways while helpfully highlighting each person that's walking around the castle and where. In the films, the Boy Who Lived finds Peter Pettigrew on the map leading to the discovery of the Animagus antagonist. He also uses the map to avoid getting caught by Filch and Mrs. Norris. The only two animals that appear on the Marauders Map are Crookshanks and Mrs. Norris. Crookshanks is part Kneazle, meaning that he's technically a magical creature. So what's up with Mrs. Norris' appearance?
It would seem that the Harry Potter films establish the Marauders Map as a tool capable of tracking magical humans and magical beasts. Pettigrew shows up on the map because even as Scabbers, he's still a person, and Crookshanks is a magical creature. Strangely, Mrs. Norris shows up on the map despite being a "regular" animal. While it's not known if Nagini or Fawkes ever shows up on the map, enough can be ascertained from who does and who doesn't appear. Therefore, Mrs. Norris must have something magical about her. Otherwise, she probably wouldn't be there. If she were a Maledictus, her presence would make more sense, given that she would technically be more human than animal.
Mrs. Norris Was Petrified
Harry Potter and the Chamber of Secrets is all about the heir of Slytherin's Basilisk terrorizing Hogwarts students. At the introduction of the plot, the trio comes across harrowing words written on the walls in blood. Hanging near it is Mrs. Norris' petrified body after a Basilisk attack. Ginny Weasley, possessed by Tom Riddle, hangs her on a torch bracket by her tail. At first, Dumbledore is unfortunately not able to revive her. This leads to quite a bit of anguish from her owner Filch and even causes him to blame Harry for attacking her. It's believed that Mrs. Norris is petrified because she sees the Basilisk's reflection in a puddle of water on the floor. However, she's the only animal to be petrified.
There are plenty of animals that wander the Hogwarts without their owners. After all, Harry first meets Neville because he loses Trevor, and Hermione often loses track of Crookshanks. Even Gryffindor house ghost Nearly-Headless Nick gets petrified by the Basilisk's stare. So out of the myriad of animals that presumably roam the castle corridors, why is Mrs. Norris the only one that gets petrified? Viewers have to wonder if a regular animal would've been able to get away from the encounter petrified rather than dead. Even though she doesn't see the Basilisk head-on, its deadly stare could be powerful enough to kill an animal even in a reflection. This would explain why spiders flee from it in droves. Luckily Mrs. Norris is revived by a Mandrake draught, notably the same one used to revive the students. This small tidbit adds even more weight to her questionable Maledictus status. If she is one, then it means she's more human than animal and would respond better to human magical treatments.
Mrs. Norris' Strange Relationship With Filch
The most obvious thing that points to Mrs. Norris being a Maledictus is her relationship with Hogwarts staff member and caretaker Argus Filch. The two are introduced together in both the Harry Potter movies and books. The pair take a divide and conquer method when it comes to tracking down any rule-breaking students. Often, Filch sends out his cat on her own, and if any student sees her, they automatically know that she will somehow "report" back to Filch. The attachment that he shows to Mrs. Norris is palpable and definitively strange. Constantly calling her "my sweet" and his over-the-top reactions to seeing any type of harm, no matter how small, befall her isn't really normal for a human and their pet or Filch's characterization in general. If anything, their relationship heavily parallels that of Voldemort and Nagini.
Like Filch, Harry Potter's main antagonist Lord Voldemort treats his pet snake better than any other living person. Nagini and Voldemort have a very personal and almost telepathic connection that bears a striking resemblance to that of Filch and Mrs. Norris. The only other animal capable of reporting back information to its owner has always been Nagini. Before Fantastic Beasts: The Crimes of Grindelwald, viewers believe that their connection is due to her Horcrux status. However, after finding out that the snake is actually a human woman, there's a lot more evidence that her humanity has something to do with their relationship as well. J.K. Rowling reveals that the Maledictus blood curse only affects women and turns them into a "beast" over time. Perhaps Mrs. Norris was a family member of Filch's, a past flame, or an old dear friend.
Mrs. Norris Isn’t An Animagus
Animagi are first introduced in Sorcerer's Stone with Professor McGonagall's character but not fully explained until Prisoner of Azkaban. Animagi are magical folk who have the ability to transform and survive for extended periods of time as a particular animal that's representative of their spirit. In order for a witch or wizard to become a registered Animagus, they must be extremely proficient in Transfiguration and undergo rigorous Ministry examination. According to the Ministry, there are only seven registered Animagi; obviously, Rita Skeeter and the Marauders don't fall into this group. While it's clear that Mrs. Norris is more than just a mean cat, there's no discernable reason that she'd be an Animagus.
With all of the new information that J.K. Rowling adds to the canon, fans are scouring over old Harry Potter content to see what might've been missed. The revelation that Nagini is a human woman suffering a blood curse definitely adds to that. After reading the books and watching the movies, one can only notice that Mrs. Norris is anything but ordinary. The evidence that she could be a Maledictus is interesting, especially when her relationship with Filch is viewed in congruence with that of Nagini and Voldemort. As well, smaller things point to this theory, such as her presence on the Marauders Map, her petrification, and the fact that she isn't an Animagus.
