Is it possible to harm creatures with Void Aura, or to disable the Void Aura? I have not been able to kill creatures with Void Aura, and have encountered them twice.

The first time is in the area with the big blood stone. I got past them using invisibility and got to the big blood stone that I destroyed. After that all the Void Aura creatures died.

The second time was when I tried to kill Cassandra. She has a Void Aura. When the battle begins she summons 5 creatures. I thought maybe the Void Aura would disappear when I killed those summoned creatures, but it did not. Thus I have not been able to kill Cassandra.

I am beginning to believe that there is no way to harm or kill creatures with Void Aura. Cassandra is kind of immortal according to the story, so it fits with that.