Other uses for communions, as MA Ermor:
Think of 3 thaumathurgs...10 slaves, 1 master. Master casts power of the spheres on turn 2. By turn 3 you cast 10 shadow blasts costing only 10D and 1S gems. That's quite some damage for the cost.
I found that having 1 master casting power of the spears on turn 2 is a must...great permanent boost for all the slaves that they keep even if you break the communion.
Another use... master one grand thaumaturgh with an air random. Have him cast power of the spheres + 8 slaves. He gets to A5 = Fog warriors, Storm, etc... basically with ermor is really easy to even get to Air and Water level 5 battlefield spells...
