Weiling Caverns (Mutanus)

Hi guys,

I've been surfing the forums for information if WC is doable. I have killed every serpent lord, yet the NPC in the beginning of the instance does not let me trigger the event to spawn Mutanus.
I've read that there were some missing bosses like Anacondra, but they are all present, so I was wandering if the event was scripted as well.

Thanks in advance =)