Another Void idea: Oblivion.
I was looking up the meaning of Oblivion recently, and to my surprise, rather than find anything related to the Void, I found more in common with memory loss. Strictly speaking, Oblivion is the point in which something is completely forgotten. Could we do something with this?
Perhaps, all of the opponent's creatures are invisible to their owner? That would be a twist. They couldn't buff the creatures, sacrifice them, or even know where on the field they are located! But the other guy would see them, and pick them off leisurely.