Another new and interesting pet...sort of...can be found while fighting the undead that are sent from the necropolises around Azeroth. This is one that stays in your bags, called a Haunted Memento. It looks like a necklace, but once you have one you will have a Shade following you around! It is very cool! It does show up on Track or Sense Undead, but you can not target it in any way. Sometimes he goes away, but usually zoning or logging in/out brings him back. He also dissappears when you summon a regular minipet.
He is not soulbound and is an item that can be thrown to another player if they have bag space. They are unique though, so if someone already has one and you throw it to them, it will be gone forever.
One other interesting note...he makes bankers vanish! I put mine in the Scryers bank and then watched as I actually waved goodbye and saw the banker go poof right before my eyes! Yikes!