Kill a Triumph Captain on the far side of the Battlescar and acquire a Fresh Brain.
My monstrosity is taking shape! All that's left is to stuff his skull with something useful.
I'm talking about brains, <name>. And here I'm going to be picky. The abomification process causes significant brain damage so it's best to start with someone smart.
One of the Alliance officers should do nicely. Seek out one of the Captains on the far side of the Battlescar and try not to damage the goods while you kill him.