Nightshade

You will never see her coming.

Nightshade serves mostly as a gag in the pilot, being spooky, emotionless and expressing her lines flatly. Should the show go beyond the pilot, Nightshade will become more prominent.

However that doesn't mean Nightshade doesn't get to shine. She's spooky without trying, appearing and scaring literally everyone in the cast (Yes, including all the bullies). No one really knows what her deal is, just that she's the most powerful person at their school. Her lines are all delivered flatly, like she does not care. (Think Sadie from The Music Freaks if you'd like a reference)