I wonder if the Dispersal Dream is something that all Shades naturally posses, or whether it is simply a Dream that can be easily taught?
I think it's a safe assumption that Alric knows more than just one Dream. Shades, on the other hand, being so closely controlled by their masters, would probably only know what their masters taught them. The Dispersal Dream would seem a logical choice. Devastating against massed troops, but not powerful enough that a Shade could use it against his master.
LR