Ezra Miller

“The truth is that Credence is magical and he’s been repressing his magic. The forces of the universe come into a physical form, which is an Obscurus, and that Obscurus initially comes to an Obscurial as a friend, encouraging them, then with increasing severity to encourage this kid to allow their true identity and true power to run through them. The idea of this Obscurus is that if you continue to repress the truth of you, it turns ugly. It becomes something actually destructive, and then it comes to this place where you can no longer run from who you are, and you can’t run from the things you’re afraid of.”

Source: Movie-Making News (page 74)