Hello.
There is a quest in a new UD spot :
A Daughter's Embrace - Quest - World of Warcraft
When you accept it, a girl will appear near you. While you go to the spot where you have to finish the quest (the tower at the end of the path), she will instantly kill every NPC that attacks you. You won't have any XP.
BUT : If you attack them first, then she kill them (Oneshot) and you get full XP. There is about 45 NPCs you can kill there with a respawn time of 3-5 minutes. When you did the entire path, just return to the begining of the path (DO NOT ENTER THE TOWER OR THE QUEST WILL FINISH).
Wait few seconds (or maybe you will not need to) and restart killing mobs again and again. Sometimes she kill them 3 by 3 so be sure to deal damages to them before she kill them.
I just made 11-15 in 22 minutes, I think it's possible to do 10-15 (or more cause NPCs are level 11-12) in less than half an hour.