Twist in the end... Spoilers!

I think the twist was what the priest's original intention was with her the entire time...not necessarily anything that happens after she wakes up in the hospital and goes to see her mom.

Exactly. *spoilers ahead*

The twist was that the priest wasn't even trying to exorcise Emma. He only pretended to! The words he says over her weren't the Ritual of Exorcism.
The demon/devil got stronger because of him, and fully destroyed everyone it could.



"I'd say this cloud is Cumulo Nimbus."
"Didn't he discover America?"
"Penfold, shush."

The priest wanted to exploit the girl to show that the devil exist by video taping everything. Then after that he would help her but it was too late and many people died.

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I was pretty surprised by the twist myself. I assumed his intentions were good and motives were pure the entire time so I wasn't expecting to find out otherwise.