Defeat the Fallen to invalidate the Vex experiment.
- Go up the slope and follow the path over to the right.
- You will find a number of Dregs waiting around the corner.
- Fight through them and follow the slope upwards. There are 2 Captains that you need to fight and defeat.
- Follow the slope upwards to find one of the 2 Rearguard Commander.
- Take your time to engage them carefully.