Fabled A Shimmering Gem Sentry  

I spent over 20 hours hunting this fabled with my high level pally with out success.
Then I bring in my lvl 75 rogue and he pops in the 3rd cycle :-(
I am starting to suspect that you need to have the rogue pop the traps in order for this fabled to pop.

I went to the back of the tunnels since there are 3 traps back there and I could easily keep all three traps cleared.

Spawns past the locked door. Placeholders are both the golems/geonids there (any) and the ones spawned off of traps. So bewarie. A Fabled may spawn on your head when you thought you were just rushing in to fight a grey.

Fortunately nothing in the zone sees SoS so you can send a rogue ahead (prolly back there to get the dagger in the first place) to trigger the traps and see what surprises are in store for you before you get jumped.