Only the mourner gear must be worn with all other equipment slots empty. Overrides and (active) auras are allowed to be worn on this achievement. After completing the Plague's End quest, the mourner gear can be re-obtained in a chest from the Mourner Headquarters in West Ardougne. The chest is in the room which was previously where the head mourner was. Using the Sixth-Age circuit's teleport to the World Gate option will bring the player a few steps away from the gate.