Pharaonic

This achievement is unlocked near the beginning of the game for defeating the Warden with the torch.(killing blow with torch, you can use any weapon to get his health down then finish him with torch)

I would also recommend disconnecting from live for this battle so that you can also earn the achievement for defeating a boss and taking no damage.(see flawless victory achievement)

Make sure you collect the Bronze sword or Mittani Sword. Free Kheti the skill trainer, run along the path until you see a wooden bridge on the right. Cross the bridge and run to the chest and get the Mittani sword. This inflicts massive damage. Also collect the Heart Plate armor. It is in a chest at the opposite end of the path with the lever. Destroy the sandbags to access the area. Remember to assign your gems before the battle.

Proceed to the warden. Equip the Mittani sword. This makes light work of him. when his health is almost depleted quickly equip the Torch and strike him to finish him off. The whole battle does not need to be with the Torch only the killing blow. This method is the easiest as the Torch itself does not inflict much damage.

The achievement unlocks upon his death however If you took any damage during this battle delete your save file reconnect to Xbox Live and get the. Flawless Victory achievement for taking no damage. I highly recommend getting they achievement with this boss as the others are too difficult.