I think that I can safely conclude that it was the Watcher rather than Soulblighter who was controlling Shiver at many points in the game and that the entire "Shiver" level was an elaborate plot for the Watcher to get rid of the Deciever. Furthermore this explains why some of Shiver's myrk giants on Relic attack their stupider brethren.. they senced The Watcher's presence in the smaller Myrks and tried to kill them. In addition.. I think the reason why soulblighter himself did not sence The Watcher's presence in Shiver was because he was sleeping with her... "times of need make for strane bedfellows, wouldn't you say Ravanna?"
- Milky
P.S. I'm dead serious about this theory Din, I hold this to be the absolute truth. I am in no way joking or being sarcastic.