Warcasters are the Mage/Generals of your Warmachine force. They are, by far, the most powerful piece in your army. They are able to pretty much wreck whatever they want, single-handed. However, sometimes they just seems so... small. With now two types of colossals available for each faction, huge battle engines, and even just "regulary" heavy warjacks, a warcaster can get lost amongst all the huge things sitting on the board. Well, that won't be a problem if you field Deneghra, the Soul Weaver.
The subtlety and Stealth of Cryx sort of goes out the window when you're riding on top of a gigantic bone and construct dragon-thing. Your enemies won't have any trouble locating her on the battlefield. And, of course, being Cryx and being Deneghra, she has all sorts of soul-gathering and soul-using abilities at her command.