One thing's for sure... we won't be seeing him around these parts any longer.
Notes
Shade of Arugal is typically the hardest of the targets. He has multiple people surrounding him at the start of the fight that can be taken out separately, but they have quick respawn timers. He also becomes invulnerable and summons adds multiple times during the fight, likely based on his health total. If you have any ranged DPS in the group who are able to fly, have them stand on the parapets along the tower and just DPS the shade to death. The shade's summons and the regular guys on guard won't be able to hit due to their melee range, but the shade casts shadow bolts and won't go into auto-evade mode. Keep anyone who can't help from the parapets away from the top floor room if you try this way.
You can accept this quest from Sasha while she is with you at Duskhowl Den, after having rescued Anya.