Poltergeist

Poltergeist: These big-headed know-it-alls have swollen brains (and egos) that afford them telekinetic power. Sadly, their sense of humor seems to be underdeveloped.

Strategy
When first encountering a poltergeist he throws books at you. You can stun him before the book is launched, but then he usually gets away. The best way to catch him is to find where he is, let him throw the book, dodge the book, and then quickly stun him. When entering the library for the fisrt time he throws books at you, but there's nothing you can do about it but dodge the books.