The last 2 parts are the hard part. You need 500 points from kills with Void damage ONLY. Kills give you 5 points ND death subtracts 2 points. I used a void shotgun and fusion rifle. Melee and grenades with a Void class also works. Play defensive as hell on Control. Aim for 12-15 kills per match with a 1 KDR or better. That should net you between 30-40 points per game. The last part has you go to a level 26 Phogoth run that has the Epic modifier, so expect a level 26 nightfall run. When you get to Phogoth kill every single enemy before damaging him. When you kill Every. Single. One. Only. Then. Attack. Phogoth. Xyor spawns on the 3rd tombship. Tombships spawn when Phogoth is at 75, 50 and 15 % health. But only. Only. If you killed enough adds from the previous wave. On roc strikes we commonly only spawn 2 Tombships because we kill Phogoth while adds are still up. If ya need help let me know.