WARNING! Contains SPOILERS for Fantastic Beasts: The Secrets of Dumbledore.
Harry Potter series. Fantastic Beasts 3 revealed Credence as Aurelius Dumbledore, Aberforth's (Richard Coyle) estranged son. But when Aberforth reunites with him, Credence is already dying because of his Obscurus curse. Credence leaves Grindelwald (Mads Mikkelsen) and s his family, albeit for a very short time, and his friend Nagini is bound to visit before he dies.
The end of Fantastic Beasts: The Crimes of Grindelwald saw Credence leave Nagini in Paris and Grindelwald in a desperate attempt to find a sense of belonging. 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 Grindelwald without putting herself in grave danger. Furthermore, it's likely Nagini felt abandoned by Credence - after all, they had escaped the circus together and were each other's closest friends when Grindelwald manipulated Credence into coming with him. However, at the end of Fantastic Beasts 3, Credence reunites with his father and goes home with him, albeit in a very weak state.
If Nagini wants to see her friend again (now that he's in a peaceful place), she will have to be quick, given Credence is dying. It's likely Nagini will find Credence in Fantastic Beasts 4, and she will try to find a cure for his Obscurus curse - as a Maledictus, she knows the tragedy of a lifelong curse and will only be more determined to help her friend. But Dumbledore (Jude Law) already said "he can't be saved," meaning that eventually, Credence will die, which will no doubt upset Nagini. Credence's loss will add to her pain, as this makes her all too aware that she will soon assume the permanent shape of a snake. Bitter and lost, Nagini will thus enter the perfect state of mind for Tom Riddle to manipulate her into doing his bidding. Losing Credence is the perfect catalyst for Nagini's dark transformation.
According to 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.
Perhaps the best thing the Fantastic Beasts franchise can do is further explore the backstories of Harry Potter characters, adding valuable information to the canon (hopefully without hurting it in the process). Fantastic Beasts 4 could potentially give great depth to Nagini's character: The Crimes of Grindelwald barely touched on her Maledictus tragedy, and there's lots to explore regarding her transformation. Showing Credence's death as the catalyst for Nagini's dark path can do the great job of connecting one era to another, moving from Credence to Voldemort and solidifying the connection between the two Wizarding World series.
