"The Crimes of Grindelwald" revealed that Nagini, Voldemort's trusted serpent, was actually once a human woman who was a Maledictus, someone fated to transform into an animal. Furthermore, as Rowling clarified on Twitter, Maledictuses are always women, as the condition is a blood curse passed from mother to daughter.
But "The Secrets of Dumbledore" completely drops Nagini as a character. It's still unclear where she went, what happened to her following the Paris rally in the second film, and what her fate is prior to eventually becoming Voldemort's most trusted companion.
Nagini, played by Claudia Kim in the second "Fantastic Beasts" film, drew criticism given that the cursed character, who eventually becomes a slave to "Harry Potter" villain Voldemort, was cast as a woman of color, particularly given the dearth of Asian representation in the series.
At the end of the film, she traveled along with Newt and company to Hogwarts, but it was unclear what happened to her in the aftermath.