I just found out this today when I was afking in orgrimmar, there is a spot where you are invisible, could be usefull for an allyraid perhaps? you cant see the health bar, target circle, nothing at all, you are completely invisble in that spot, also you cannot be attacked by guards etc because youre evading.
check it out
The easiest way to get there is by slowmotionwalk, its a very thin spot but not to hard to get to, gl