In Reikland, if you go to the PQ Hunting the Hunters, there is a stairwell at the front of the towers. If you stand on the rail and get enemy mobs on the rail with you, they can't hit you but you can hit them. Here's a video of it in action:
[ame=http://www.youtube.com/watch?v=aTsWUZBSI0M]YouTube - Reikland Mob Exploit[/ame]
Works on every mob there, to include champions and heroes.
Destro only as far as I know though.