So when we went to see the movie, my brother turns to me and goes "why the fuck does Newt have a fucking dementor in a bubble?" Obviously we then learned that it was an obscurious, but now I can't stop thinking about it.

When the aurors attacked Credence and blew him up, they thought they were eliminating the threat an adult obscurial posed. But instead, all they did was force Credence to level up, in a sense. And now they've got a very pissed-off dark creature that eats souls on the loose. And he's got one hell of a grudge.