This is based on opinion. Please don't list it on a work's trope example list.
Nightmare Fuel / The Devil's Advocate
Good Lord, it's everywhere. Most notably when Kevin's wife goes out with the business partners' wives and finally sees that they are actually demons in disguise. And the baby playing with the ovaries. If that's not enough, there's always every single facial expression Al Pacino has in this movie.
The slightly dumpy woman that guides Kevin through his time at the law firm seems as human as anyone. She's not overly attractive, like Tamara Tunie or Connie Nielson, and she isn't strictly implied to be super-smart with the law, though it could be since she works there. Unlike the others in their mask-drops, which have all shown demonic mouths and eyes, she just smiles a creepy, broken smile full of demonic teeth, as if to say that she doesn't need to drop the mask entirely. And then, when Kevin goes to meet Milton after Mary Anne has slit her own throat, she tells him in the exact same motherly tone she's used throughout the movie that he's waiting for Kevin and he'll take that fear away.
The scene where Mary Anne snaps and commits suicide by slicing her throat with a piece of broken glass.
Her gradual breakdown leading up to her suicide as a whole can be considered this.