Boardgamegeek user Michael (Zwerg) has posted an in-depth guide on Filch as the first in a series of tips, strategies, and analysis on the Mice and Mystics crew.  As a veteran of the series, I was impressed with how in-depth and thoughtful his analysis is, and it brought certain aspects of Filch's playstyle and best uses into sharp relief.  Check it out at the following link:

Zwerg is currently taking suggestions for the next character that he will write a guide for, currently Maginos is winning so feel free to vote if you'd like to get your own favorite character next in line!