Mosh Pit

Here is one strategy, confirmed that it work.

1. 
   
2. Pull the boss
3. 
   
4. Pop Heroism, Bloodlust or Time Warp and burst the boss to at least 30%
5. 
   
6. During this phase the tank must take the two adds
7. 
   
8. When Harlan is about to Blades of Light return to the entrance of the room
9. 
   
10. During this phase the tank must take the two new adds, at this time you got 4
11. 
    
12. Before Harlan reach you, the healer must jump into the pit and the rest of the group have to go near the flag next to the wall on the opposite ramp and wait to get caught by Blades of Light
13. 
    
14. Pop survival cooldowns
15. 
    
16. Get caught in Blades of Light
17. 
    
18. At this time you are 8 in a very short version of Harlan's Blades of Light and your healer is able to heal
19. 
    
20. Finish the boss before another Blades of Light
21. 
    

If another Blades of Light happen and just one player/mob get caught it will fail.

You don't need to kill the adds with Blades of Light, you just need to get 8 players/mobs caught by it, and then kill the boss, as the achievement says.

Works best while affected by [spell=101261]

Ok guys this achievement is easy at lvl 110. Just go to the boss with all adds possible, start the fight and stay on the top/entrance. Boss will call for extra adds and when he casts [spell=111216] just wait him on the top with adds. Use addon RaidAchievement and you will know when the requirements are completed then kill boss.