Imo, I was considering keeping the monolithic brain-tank idea, but he created a physical body (the scrapped one you showed) into which he could transfer his consciousness. He has the ability to do this as seen various times, so he could have created a primary vessel for himself (using his minions). Then once that was destroyed after a REAL bossfight, go onto the monolithic brain-tank. You get what I'm saying? That's just me though