Though we don't learn much more about the nature of the Obscurus in Fantastic Beasts: The Crimes of Grindelwald, we do get a stunning reveal about Credence's origins that more or less confirms that Ariana Dumbledore was also an Obscurial. In the final moments of the movie, a chick that Credence has been taking care of abruptly becomes a phoenix - the symbol of the Dumbledore family, reputed to appear whenever a Dumbledore is in need.
Yes, as Grindelwald explains, Credence is indeed the "son cruelly banished," from the prophecies of Tycho Dodonus, but he wasn't (as he previously believed) banished from the Lestrange family. His real name is Aurelius Dumbledore, and he is the younger brother of Albus Dumbledore. Credence was lost when, during a stormy sail across the Atlantic, Leta Lestrange swapped him in his crib with her own brother, Corvus Lestrange. Corvus (believed to be Aurelius) subsequently drowned when the ship sank, but the real Aurelius survived and ended up in an orphanage with a new name: Credence Barebone.
The fact that Aurelius is Ariana Dumbledore's brother reinforces the theory that Ariana had an Obscurus of her own, and that the condition can apparently run in families. In both cases, the trigger appears to be some kind of trauma at a young age: for Ariana, being attacked by the group of muggle boys; and for Aurelius, the abuse he endured at the hands of Mary Lou Barebone. It may even have been the shipwreck itself that traumatized Aurelius, even though he was only a baby. Either way, it seems that the Dumbledores have a predisposition to manifesting this dark force as children.
Fantastic Beasts: The Crimes of Grindelwald also sees Credence/Aurelius manifesting his Obscurus in interesting ways. At the start of the movie, Credence has made his way to Paris, where he hopes to find his birth mother. Instead, he finds Irma Dugard (Danièle Hugues), a servant to the Lestrange family, who signed her name on his adoption papers. Believing Credence to be the baby that she gave away all those years ago, Irma embraces him - offering Credence the kind of love that he never experienced as a child.
However, that moment of joy is short-lived. One of Grindelwald's agents, Grimmsonarrives at Irma's apartment and casts a killing curse that strikes her dead. A grief-stricken and furious Credence unleashes his Obscurus, tearing the building apart in a desperate effort to kill Grimmson - who is prepared for the outburst and manages to fend the Obscurus off.
We see the power of the Obscurus again after Credence learns his true identity. Grindelwald hands him a wand, the first that Credence has ever owned, and Credence channels his rage at Dumbledore's perceived betrayal. Seemingly drawing on the Obscurus, he blasts a hole in the side of Nurmengard Castle, with the wave of pure power continuing onwards and blasting apart the side of a mountain. With Aurelius Dumbledore (and an Obscurus) at his side, Grindelwald is now a greater threat than ever before.