Thought I'd share for every mage running around on a solo mission to do as much quests as the achivements say they shall..
This is how mirror image helps you when killing mobs that would down u normally.
If you start up with like Pyro/frostbolt/arc blast and a fireball, the elite is starting to get close to you..
Use your mirror image spell and 3 copies of you start attacking the target.
Tho they have faily low hp, they "taunt" the target to attack them wasting 2 hits from the elite for every copy you have and gives you time to either run further away or just nuke him down. I've tried to overaggro them, but dosn't seem to be possible. =)