The easiest way to defeat Faustus is to block until your Fury bar glows and hit him with that. Dodge every time you see him try to use a glyph attack. It only takes two Fury hits to get him to go to the furnace room. Load up the Mist glyph and head to a steam spot immediately. You should be able to turn on the furnaces without taking too much damage running from steam spot to steam spot. Once he gets burned and starts running around the rafters, just run around the edges of the room until you hear him drop down. Try to be near a corner or wall. Wait for him to jump at you, then jump or dodge his attack. Once he hits the wall, he will be stunned. You can hit him with a good combo before he jumps back up to the rafters. Repeat this two or three times and he will die quickly.