I'm just drooling thinking about allying in Fateweaver + anything (say some token bloodletters) into a CSM army. Fateweaver is a little less broken in Daemons than he could be because not many Daemons have good armor saves (thus "Fatecrusher" was born). In an army full of 2+ and 3+ saves, Fateweaver would be way beyond ridiculous.