Shadow Labyrinth Key

Shadow Labyrinth Key opens the doorway to the instance Shadow Labyrinth.

Source
The Shadow Labyrinth Key drops from Talon King Ikiss in Sethekk Halls. It is available to everyone in the party who does not already have it.

Patch 2.3.0: "The Shadow Labyrinth Key can now be looted from the Talon King's Coffer next to Talon King Ikiss in the Sethekk Halls"

This key is only to open the south gate in Auchindoun towards the Shadow Labyrinth. It is not necessary to have the key in your possession to enter the instance gate.