Nagini didn't appear in Fantastic Beasts 3 - most likely because of Claudia Kim's pregnancy amidst the Covid-19 pandemic, but this also makes sense in-universe, as she couldn't have come close to
When Fantastic Beasts was announced, fans presumed familiar faces from Harry Potter would appear. However, Nagini was on nobody's list of characters they'd like to see in a prequel. Not because she wasn't well liked - it's that she didn't have enough of a character to have an opinion on.
She's genuinely there for him every step of the way, and that means a lot to him. The Crimes of Grindelwald's climax sees Credence leave Nagini behind to join Grindelwald and learn his true identity. She then appears alongside Newt and his allies, implying she'll take their side in the upcoming war against Grindelwald.
There's been speculation he may have found her while in exile in Albania between 1981 and 1994, where he assumed a phantom-like form and possessed many animals (however, only snakes could bear him inhabiting their body). This could have something to do with his propensity to speak Parseltongue.
More research proves that Alison was pregnant while filming, which could also explain things. Another fan noted, "Weight gain can truly change a person like night and day, even eyes and eyebrows can look vastly different!" Sadly, in April, Alison revealed that her pregnancy resulted in a miscarriage.
It was such a heavy time, and there was such a reduction of socialization as for being able to, like, see other people, and I was pregnant all throughout the film, and Victoria Yeates [Bunty Broadacre, Newt's assistant] was also pregnant on the film and because we weren't able to do any classes or any kind of in-person ...
Alison Sudol uprooted herself from L.A and moved to London to play Queenie in the Harry Potter prequel Fantastic Beasts: The Secrets of Dumbledore.
Nonetheless, despite her initially benevolent nature, Nagini's blood curse eventually turned her into a snake permanently. Though it is unknown if she became evil as a result of that, or was turned evil as a result of Voldemort turning her into a Horcrux. As a snake, Nagini was completely loyal to Lord Voldemort.
When Harry and Hermione are on the first floor of Bathilda's house, Nagini (inside the corpse of Bathilda) tells Harry to "Come!" from the next room in Parseltongue. In reaction, Hermione jumps and clutches Harry's arm, and the two of them obey the command.
It wasn't just inanimate objects that could become Horcruxes. Lord Voldemort's beloved snake companion, Nagini, was also transformed into one, and Dumbledore seemed to know it, ominously predicting that a day would come where Voldemort would 'fear for his snake'.
Nagini is loyal to Voldemort because he can speak with snakes. As a Maledictus, there probably isn't much time after the events in The Crimes of Grindelwald before Nagini falls to her blood curse, becoming a snake forever.
Nagini was a maledictus. That means that she carried an innate, hereditary blood curse giving her ability to transform herself into snake, which gradually became uncontrollable until Nagini eventually lost the ability to turn back into human completely.
Nagini, it turns out, was actually a Maledictus—a witch with a blood curse that turns her permanently into a beast (in her case, a giant snake). In the film, the witch is played by Claudia Kim.
Unless one or the other has a significantly smaller role in the films than we are led to believe, Dumbledore and Nagini will get to know each other. From the very little we see of Nagini, it looks like she's at least potentially on the same side as Dumbledore.
Because of this, Nagini was born a female 'Maledictus' - one who carries the Maledictus curse. A 'Maledictus' suffers from a blood malediction- a type of curse that causes the sufferer to slowly transform in to an animal over the course of their life. The animal can vary according to the specific curse.
This was an ability the Circus Arcanus took extreme advantage of. Ultimately, however, Nagini's Maledictus blood curse took over, which forced her to stay in her snake form permanently.
Erroneously believing Snape is the master of the Elder Wand and that Snape's death will make him the master of the Wand, Voldemort kills Snape by having his pet snake Nagini bite him through ...
Nagini seemed integral to Lord Voldemort's survival before he could be restored to his body, and we learnt, quite grotesquely, that Voldemort even tasked Wormtail to 'milk' Nagini so he could live off her venom to keep his strength up.
Of course, Voldemort was a Parselmouth, and this was the root of his friendship with Nagini. Much like Grindelwald did with Credence, it's likely Voldemort gave Nagini a false sense of belonging after she had been trapped in a snake's body for possibly decades.
And unlike with Harry, Voldemort did say the spell when he killed Bertha Jorkins to make Nagini a Horcrux. When Voldemort fell at Godric's Hollow, he had split his soul into six parts, and Nagini is to be the seventh to reach his goal. But Voldemort never knew about the Harrycrux.
Once he learned that his horcruxes were being hunted, he knew Nagini was at risk. He couldn't know how his enemies had been able to find his other horcruxes, but he had to suspect at the least the possibility that it was by some magical means unknown to him, perhaps devised by Dumbledore.
Though it may later be revealed that the Dark Lord did indeed know that Nagini was a Maledictus, there's currently no indication that he (or anyone else) ever thought that she was anything other than a snake who was made into one of the Dark Lord's Horcruxes.
After a brief argument, Queenie agreed, and Newt lifted the spell. Jacob refused to marry her, fearing that she would be punished for marrying a No-Maj.
Lestrange is the surname of an ancient Dark wizard family. The most notorious Lestrange from the "Harry Potter" series was Bellatrix — the cousin of Sirius Black and Lord Voldemort's most devoted follower.
Queenie Goldstein: An American witch and the younger sister of Porpentina Goldstein.