Obscurus

"It's an unstable uncontrollable dark force that busts out and attacks, and then vanishes."

- Basic description

An Obscurus was the manifestation of the repressed energy of a magical child (known as an Obscurial). Described as a "dark" and "parasitic" force, an Obscurus was created when the child in question was forced to repress their talent through physical or psychological abuse. This energy could manifest itself as a separate entity that can erupt in violent, destructive fury.

Description
When an Obscurial lost control, the Obscurus force was released, often focused on the cause of the Obscurial's torment, but also causing destruction in its wake.

The Obscurus could be largely invisible or appear as a flying, incorporeal, and amorphous entity with the appearance of a black, fluid-like cloud, or a violent torrent of darkness, sometimes with a reddish core. Some described it as a "dark wind" or "dark mass" with "shining white eyes". Its appearance could be oleaginous, or "rich in, covered with, or producing oil, or oily or greasy". There have also been instances when a face briefly emerges from the shadowy entity, or a white glowing image of the host appears inside of it.

The size and might of an Obscurus depended on the innate power of its host; the more powerful an Obscurial, the more powerful their Obscurus. When an Obscurial reached their emotional and mental breaking point, they could lose control completely and physically transform into an Obscurus. Its size and mass at specific times may also have be connected to the level of negative emotions that triggered it at that instance, as well as the current mental state of its host.

In this state, they are enormously destructive to their surroundings, to the point of causing objects to levitate or break without physically being in contact with them. This notably causes damage to structures and objects near the host. However, they could be calmed down by someone they trust, which caused them to revert to their corporeal state, though being emotionally conflicted could cause the Obscurial to transform back and forth.

An Obscurus often targeted people that are the source of their host's distress, as Credence Barebone's Obscurus went after Henry Shaw after he was insulted by him, though it took longer to attack Mary Lou Barebone since Credence was so close to her. When his adoptive sister ran in fear of him and Gellert Grindelwald, in the guise of Percival Graves, stated that he had lied to Credence about taking him in as a wizard, Credence lost control completely of his Obscurus, causing wide-spread damage in New York.

When an Obscurus killed someone, it left specific marks on the victim's body, largely focused on their face.

When the host Obscurial died, the Obscurus typically vanished along with them, though Newton Scamander successfully kept one alive when its host died by encasing it in a magical field.

Other mentions
Obscurus Books was the wizarding book publisher based in Diagon Alley, that published Newt Scamander's.

Appearances

 * Fantastic Beasts and Where to Find Them: The Art of The Film
 * Inside the Magic: The Making of Fantastic Beasts and Where to Find Them
 * Fantastic Beasts and Where to Find Them: The Art of The Film
 * Inside the Magic: The Making of Fantastic Beasts and Where to Find Them
 * Inside the Magic: The Making of Fantastic Beasts and Where to Find Them

Notes and references
Obscurus Obskurus オブスキュラス