Hey, recently my friend told me about this in game and I thought I'd share it with you. These mobs have a very strange respawn timer. They will respawn almost instantly after you kill them and they have a VERY nice droprate for Netherweave Cloth. Very useful for farming bandages for arena. Also they have a normal droprate of green items, which are nice to vendor or disenchant.
Shadow Council Warlock - NPCs - World of Warcraft
Shows their location and loot. There are only 12 of them up at a time but I've literally had 5 other people there with me and none of us had to wait to kill. They also have very low hp and damage. Only about 5,000 health and their Shadowbolts hit for about 500-600 if I remember. Good luck farming!
Edit: I searched forums for the mob name and only found them associated with Aldor Rep farming... but they drop a TON of Netherweave and respawn very quickly so...thought I'd post this.