Monsters and their immunities.
1. Dread Minion: Bronze
2. Dread Minion: Cenequus
3. Dread Minion: Guarnob
4. Dread Minion: Judge - Physical Immune
5. Dread Minion: Blood - Physical Immune
6. Dread Minion: Soul - Physical Immune
7. Death Knight: Doom - Physical Immune
8. Death Knight: Naught - Physical Immune
9. Tyrant: Flamol - Fire Immune
10. Tyrant: Icika - Water Immune
11. Ancient Sand Fiend - Earth Immune
12. Tyrant: Tornada - Physical Immune, Earth Immune
13. Requiem Tower - Physical Immune, Metal Immune
14. Dread Servant: Blade - Physical Immune
15. Dread Servant: Edge - Elemental Immune
16. Dread Lord: Hengchih
17. Death Knight: Dimensic - Physical Immune
18. Death Knight: End - Physical Immune
19. Soul of Thromh the Mighty
20. Rend Razorjaw's Soul
21. Poison Tail Occultist's Soul
The ideal spot for this event would be at #20. At that spot you can have members lure both Ancient Sand Fiends, Poison Tail Occultist, and Soul of Thromh the Mighty to Rend Razorjaw. As far as I know none of these mobs aoe, all are physical, and all can be damaged by physical damage. So with proper luring you could set up a zhen to kill them.