When Mithrax speaks to you this time, his tone is different. His usual spiritual optimism is tempered by foreboding.
He feels a malevolent force pulling from the center of the Vex network—the same force he noticed when you first stepped into the network on Europa. He fears the Vex are being manipulated somehow, and that the Endless Night has a greater purpose than he initially thought.
"Darkness is coming for you," he warns. The Vex must be disrupted before it is too late.