A new, dark magic introduced in 'Fantastic Beasts' may explain one of the biggest mysteries in 'Harry Potter'

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Ezra Miller as Credence Barebone in "Fantastic Beasts and Where to Find Them."

Warning: This post includes major spoilers for "Fantastic Beasts and Where to Find Them."

Part of the fun of J.K. Rowling's "Harry Potter" series is learning about her magical universe. Every new book introduces new magical concepts she invents. In "Harry Potter and the Chamber of Secrets," it's the basilisk and Chamber of Secrets. In "Prisoner of Azkaban," it's dementors, time turners, and patronuses. And so on.

In "Fantastic Beasts and Where to Find Them," Rowling's new "Harry Potter" movie spin-off series, the author continues that tradition. The big new magical concept she introduces is the Obscurus.

An Obscurus is a type of magical parasite that forms when a wizard or witch suppresses their magical ability. If they don't perform spells, it's as if their magic turns inwards and eats at them.

Obscuruses eventually take over their host bodies. The parasite itself is called an Obscurus, and the person whose body is used as a host is an Obscurial. If they're not controlled, an Obscurial can be extremely dangerous.

An Obscurus looks like an ash-colored, tendril-equipped cloud. When an Obscurial loses control, they take a similar form. You can also sometimes catch a glimpse of a face inside them.

In "Fantastic Beasts," we learn that Scamander captured an Obscurus.

The first Obscurus we see onscreen is in the custody of Newt Scamander, the main character of the "Fantastic Beasts" series. Jacob Kowalski, a No-Maj (an American-English term a non-magical person) who Scamander befriends, is hanging out in Scamander's briefcase.

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Percival Graves enlists Credence Barebone to help him find an Obscurial. Little did he know...

The briefcase is magically expanded into an enormous space inside, and it looks something like a cross between a movie studio and a zoo. It's divided into different sections, each one a different habitat for Scamander's animals. One of these sections is a blisteringly cold, snowy landscape.

Inside is an Obscurus floating in a transparent bubble. It looks like it's about two or three feet in diameter.

Kowalski appears entranced by it, but Scamander warns him to step back. Scamander says he captured the Obscurus in Sudan three months earlier. It apparently killed a girl or woman - "He was eight when she died," Scamander said. Obscurials rarely live past the age of ten, and they were more common centuries earlier, when wizards and witches had to hide their powers from their No-Maj neighbors in fear of persecution.

An Obscurial kills a No-Maj, threatening the secret magical community.

As in the "Harry Potter" series, the magical community in "Fantastic Beasts" - which is set in 1926 New York - is hidden from the non-magical community. MACUSA (Magical Congress of the United States of America) is even more secretive than the Ministry of Magic at the time, forbidding contact between No-Majs and magical folk.

From the start of the film, MACUSA is on high alert. A mysterious magical force - some suspect it's a beast, some suspect it has something to do with Grindelwald - is ripping up New York City and then disappearing. Percival Graves, MACUSA's head auror (magical law enforcement officer), is on the case. By it's description, it seems to be an Obscurial.

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An Obscurial attacking New York City.

Later, an Obscurial - possibly the same one - breaks into a dinner in honor of Henry Shaw, Jr., a New York Senator. While Shaw is giving a speech in front of an audience of fat cats, it lifts him up in the air and kills him.

Scamander analyzes Shaw's body and recognizes by the marks on his face that he was killed by an Obscurial. Before Scamander found one in Sudan, one hadn't been sighted in 200 years.

The No-Majs, meanwhile, suspect that something is out of the ordinary. Some begin to entertain the previously fringe theory that there's magic in the world. The secret world of wizards is at risk of becoming known to the public.

Credence Barebone turns out to be an Obscurial.

Graves enlists Credence Barebone to help him find an Obscurial. Credence is an orphan who, along with his sister Chastity, is adopted by an abusive No-Maj anti-magic activist, Mary Lou. Graves had a "vision" that the Obscurus was a young girl, about ten years old.

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Obscurials can ooze down walls. Here it is in the City Hall subway station.

It's thought that one of his younger sisters Chastity or Modesty may be the Obscurial throughout the movie; however, it turns out Credence was an Obscurial all along. He's more powerful than the usual one, because he's a teenager, much older than the usual Obscurial host body.

What we don't find out is whether or not one of Credence's sisters may also be Obscurials. Chastity had a fake wand which she may or may not have been trying to practice magic with. We know she's Credence's biological sister, so she has magical lineage.

And what about Modesty? She's identified as having magical powers, and she and Credence call each other brother and sister even though they're not related by blood. Why? And why did Graves think she would have magical powers, anyway, if they're not related by blood?

Whether Modesty or Chastity are also Obscurials, in addition to Credence, we don't know. We don't find out what happens to them. And so we're also not sure if it's Credence, or either of them, who are responsible for earlier Obscurial attacks on New York City.

Grindelwald wanted an Obscurial to expose the magical community.

At the end of the movie, we learn that Graves was Gellert Grindelwald, a powerful dark wizard, in disguise.

Grindelwald believes that the laws keeping No-Majs and magical folk apart benefits No-Majs at the expense of magical people. He wanted to find an Obscurial and unleash it on the world. Doing that could have started a war between magicians and No-Majs, through which Grindelwald could win and impose a magical ruling class over humankind.

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Obscurials are dangerous.

In the end of the movie, though Credence, in Obscurial form, is defeated, a wisp of him escapes, presumably due to return in future movies. Could Grindelwald find a way to break free from MACUSA to continue his Obscurial hunt?

Obscurials and the connection between "Fantastic Beasts" and the "Harry Potter" series

The concept of an Obscurial can help explain a fuzzy moment in the "Harry Potter" series.

The death of Ariana Dumbledore, Albus Dumbledore's younger sister, tore apart Dumbledore's and Grindelwald's friendship. But it's not totally clear how it happened.

We know that Ariana died when she was 14. She was known to be sick. She never attended Hogwarts or went to St Mungo's Hospital for Magical Maladies and Injuries. Instead, her brothers Albus and Aberforth cared for her. Muriel Weasley speculates in "Harry Potter and the Deathly Hallows" that she was a squib and that she was responsible for the death of her mother, Kendra Dumbledore.

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A portrait of Ariana Dumbledore from "Harry Potter and the Deathly Hallows: Part 2."

Later in the book, Aberforth Dumbledore, Ariana and Albus's brother, gives a clear assessment of her life. When Ariana was six years old, she was attacked by Muggle boys.

"It destroyed her, what they did: She was never right again," Aberforth said. "She wouldn't use magic, but she couldn't get rid of it; it turned inward and drove her mad, it exploded out of her when she couldn't control it, and at times she was strange and dangerous. But mostly she was sweet and scared and harmless."

...

"[If] the Ministry had known what Ariana had become, she'd have been locked up in St. Mungo's for good. They'd have seen her as a serious threat to the International Statute of Secrecy, unbalanced like she was, with magic exploding out of her at moments when she couldn't keep it in any longer."

That sounds... exactly like an Obscurial! An Obscurial is a magical person who doesn't perform magic. It makes a person strange and dangerous at uncontrollable times, with magic exploding out of you. And it's definitely a threat to the International Statute of Secrecy.

To keep Ariana safe and quiet, the family moved to quiet Godric's Hollow. When she was fourteen, "she had one of her rages" and killed her mother. Aberforth regrets he couldn't be there to calm her down. And in "Fantastic Beasts and Where to Find Them," Scamander and Tina Goldstein try to calm down Credence Barebone as a way to help him control the Obscurus taking over.

Warner Bros. Pictures

Aberforth Dumbledore.

As an Obscurial, Ariana was someone who didn't perform any magic, so it makes sense that people would think she was a squib. Graves, too, thought Credence was a squib.

In a three-way duel between Grindelwald, Albus, and Aberforth, Ariana tried to intervene to stop it, but she was accidentally killed.

The whole affair explains why Grindelwald would be looking for an Obscurial, or how he knows how to recognize one. During "Fantastic Beasts," one wizard remarks that they haven't been seen in centuries. Well, maybe Grindelwald saw one and knew what to look for.

Unleashing an Obscurial would be, in the words of Aberforth, "a serious threat to the International Statute of Secrecy" - which is exactly what Grindelwald is looking to do. Once magicians are public, he could pit them against non-magician-kind.