The Cabal on Mars plan to use the psion flayers to use Phobos, as a weapon, potentially attacking earth. Several story missions will lead up to you finding the location of the cabal emperor, Brachu'urn Thalus. The image shows my theory of how the fight will pan out. The emperor (Immune), is standing in the middle is sheilded by three psion flayers (Who resist all attacks with the incorrect damage type) two to the sides and one in front. There are also doors to the side that will release cabal (Phalanx, legionary, centurion, collosus). The middle psion flayer is the most important however. Once you take out the flayers the psion mind will power Brachu'urn.You will recieve the "Psions power" buff and will be able to damage the emperor. He will be immune to all damage not of the type the middle flayer was(Arc, solar, void). If you do not take out 1/3 of his health the psion mind will "overheat" and kill everyone. If you can take out 1/3 of his health the psion mind will lose the its power for that damage type. 3 more psion flayers will emerge and you'll Rinse and repeat with all 3 (Void, solar, arc) until you kill the emperor (3 runs). The psion mind will be destroyed, the emperor will be dead and you will be now be able to claim your rewards. Leave some feedback on what you think.