(2) Set: Increases the damage done by your Unstable Affliction by 20% and your Immolate by 10%. (4) Set: Increases the critical strike chance of your Shadow Bolt and Incinerate spells by 5%.
The long "nose" and hood of the piece suggest influence by history, during the Black Plague where the priests, which were more like warlocks in their methodology, would wear bird-like hoods filled with herbs to try and ward off the plague.