These guys create the Tortured Souls out of the corpses in the pit, so if you want as many mobs as possible, let them alive and they'll spawn some new ones for you.
A War Wraith says, "Awww, come on guys, this isn't funny! There's something stuck to my face! Come on, where am I?... OW!!! I tripped... I'm gonna tell on you guys!... OW!!! Aw crap..."