Before anyone says repost, ive checked as much as i can searching for this and have found nothing. If its a repost sorry, anyway onto the bug/exploit.
-----> Will edit with pics, once it has reset. <------
This exploit/bug is used for herald volazj, the last boss just before the exit to the instance.
Right, basically to the left and the right of the boss there are pillars your group needs to be close to the right pillar and so do you tanking the boss. When he starts to cast insanity the whole group moves LOS of the boss, meaning the that clones of the group kill each other straight away meaning you skip the insanity phase and getting the 2 min achievement kill.
As said i will post pics asap tommorow, to give a better understanding of whats said above.