Since 5.3, Kor'kron guards have come all over the place. In Durotar there's a bunch of NPCs, "Kor'kron Grunt" patrolling around, on the road down the the harbor. Those mobs are neutral, got 3.9m health, got a frontal channel AoE and are very easy to kite.
What you do, is that you pull one of them (pull all of them and you need to be good at kiting), kite him inside Orgrimmar, stand right on top of an AFK guy or low lvl and wait for the Grunt to start casting Wild Cleave. Wild Cleave hits my warlock for 30-40k/swing, and it does around 5 swings per turn. It got around 8 seconds cool down.
It's much prefered that you use a class that can tank a mob for a while, because they really hurt on clothies (so either have good damage migration or good absorbs, it broke my Fury Ward in 3 hits (67k absorb)). Other people can attack these mobs at any time, so it won't last forever.
NOTE: You most likely must be lvl 90 to see these mobs in Durotar, as they're probably part of the Escalation phasings (havn't tested on lower chars).
You can also use this to kill people in duel if your server is populated.
Enjoy it while it lasts.