When Mary Lou said that Credence's mother was a "wicked, unnatural woman," she had no idea how right she was. Credence was the result of a boggart attacking a man who was absolutely terrified of women, or something like that.
This biological background was what allowed him to have control over the obscurus for as long as he did, but eventually even that would have failed him, and it probably would have killed him.
Luckily for him, Credence wasn't the first half-human/half-boggart Newt had come across.
Wherever you want to take this is cool with me- it can be cracky, with Credence learning belatedly that oh shit, he can shapeshift into something that ISN'T the obscurus. It could be angsty- being magical would have been bad enough, but learning he's the literal bogeyman? Or, you could give poor Credence a little love, and have his partner actually like the fact that he can change forms at will.
Any/Credence, Credence's Mother Was A Boggart
This biological background was what allowed him to have control over the obscurus for as long as he did, but eventually even that would have failed him, and it probably would have killed him.
Luckily for him, Credence wasn't the first half-human/half-boggart Newt had come across.
Wherever you want to take this is cool with me- it can be cracky, with Credence learning belatedly that oh shit, he can shapeshift into something that ISN'T the obscurus. It could be angsty- being magical would have been bad enough, but learning he's the literal bogeyman? Or, you could give poor Credence a little love, and have his partner actually like the fact that he can change forms at will.