The Priest of Sorrows is the monk of the Stone Summit deep inside the Shiverpeaks. Because they use the spell Resurrect, as well as the powerful spell Mark of Protection, they are a priority target for any group.
These are the most troublesome among the Stone Summit units inside the Furnace. The reason for this is their Resurrect skill. They will alter how you kill groups and how you lure them simply by being there.
Whenever they are in a group they will stroll around, and if they come within range of an ally's corpse (an ally to them), they will resurrect it, undoing what was done. They are most dangerous around bosses as they will keep resurrecting them. Unlike most monks, they give precedence to resurrection over healing.
The Resurrect that the Priest of Sorrows use is different from the one that is accessible to the player. Despite it looking like the normal Resurrect, it actually has no recharge time. This leads to them continuously attempting to resurrect their allies even though their Resurrect has been interrupted. This can be used to your advantage, when they start to resurrect their allies, they won't be able to heal or put the annoying Mark of Protection on anyone which makes defeating them much easier. It is best to interrupt them when they're nearly finished casting resurrect.