Why is Sister Mary Eunice still called Mary Eunice even in flashbacks where she's a teenager? When nuns are named "Sister Mary <something-something>" it's usually as the name they took when they took holy orders.
Or if they had traditional Catholic parents.
Did the Enfant Terrible get away with her crimes? Wouldn't the police find it just a bit suspicious that her entire family was killed in the same manner as her friend was earlier? That she is claiming the same man who killed said friend also killed her family? They must have some file about the case somewhere. Surely someone is going to notice the similarities?
The killings were only a few months apart IIRC, so it seems like the same file should still be open and probably would be worked by the same cops. They might very well find it suspicious, but the girl is outside the narrative at this point.
...What exactly did those aliens want, anyway? They seemed to go to a lot of trouble for two of their test subjects to die, one of them to get pancreatic cancer and their kids to become a lawyer and a neurosurgeon.
In the end the point seemed to be creating those schizophrenia curing kids. Based on past stories with aliens creating human-looking kids, it is probably the prelude to an alien invasion.
Why did that prisoner look like the Angel of Death?
Sister Jude had lost her mind and imagined that the thug inmate was the Angel of Death come for her.
Why did the Devil/Demon act pretty feminine when it possessed Sister Mary Eunice? Does it take on gender traits?
During The Devil's brief lapses in control, we find out Mary Eunice is at least aware she's possessed, which means she could be aware of what The Devil is doing with her body. The Devil was likely acting sensual to further upset the neurotically chaste, "gynephobe" Sister Mary.
When Lana escaped from Briarcliff with the tape and got into the taxi why didn't Dr. Thredson alert the taxi driver that she's an escaped patient and take her back in there at the taxi driver's relief and approval? Even if she did start screaming and yelling that he's Bloody Face it would have sounded like insane rambling. Or would someone inspect the tape either way? though he could have taken it.
This bothered me as well. Revealing herself to him while he could easily have waved the taxi driver to a stop was idiotic on her part, and on his for just standing there as if he was not mere feet away from her.