Touch the torch again (make sure you touch the same torch you used to spawn him) to receive the Shadow Flames (key item).
If other players in the party also need this key item, they can touch the torch as well - you don't have to fight him for each person.
Head back to Port Jeuno and click on the ??? at the toolbox for a cutscene. This completes the quest.
The Rest[]
Guslam mentions something about armor scattered about Vana'diel. You can find two more pieces of armor by simply opening coffers in the following zones: