Rift Quest:Watchers Above  

As you approach each of the Spyglasses, a Golden Maw Operative will emerge from hiding, stun you, and attack. They are also found, hidden, all over the Scoured Ledge, even away from the spyglasses. There is one by each Spyglass and a few roaming the area.

The trick with these guys is to creep forward till you see his stealthed form appear, then smack him with your fastest ranged attack. This will pop him out of stealth and his stun requires that he be in stealth to use it!