Void aether is the technology developed by the Baltiks as they fought to survive in the Dark Below. Without access to pure aetherite, they were forced to improvise in the development of their own from the materials at hand. This produced a dirty, twisted version of aetherite which generates immense aetheric potential but also creates a toxic residue that twists the darkness into those who use it.
The immediate consequences of exposure to void aether residue is a lingering weakness and sickness. After this, the victim begins to twist and warp themselves as the void aether begins to mutate them.
The Baltiks have used this effect to create their warped shock troopers and also to mutate beasts of burden to increase their potency.