Go out to Phogoth's room and kill everything but Phogoth, only shoot him until he breaks his chains and afte u killed everything else. Wait a while then drops ships will come in, go back to the room just before Phogoth, if u are in that room for 15 sec (something like that) a seeker and wizards spawn so go to the room just before it. The enemies from the drop ships will flood into the seeker room but won't go any further and just camp there un xyor comes, after u kill him, u can quit or kill Phogoth but either way u for thorn.