Hi all! My first post here. This isn't really an exploit, but "creative use of game mechanics" I guess.
It's easy as pie really. Go to Gadgetzan, A-52 or any other neutral town.
Make a portal to IF or wherever. Then pyroblast, fireblast, etc. Hit the enemy with all you got.
The guards will run to you, but you will have a window of 4-5 seconds to kill the enemy.
When you are low on health simply click the portal and *boom* you are safe.