This is so going to be nerfed.
I'm sorry, I don't mean to be negative, but holy cow. For thirty seconds, this spell makes you a God.
Here's what Mirror Image does:
When used, it instantly conjures three copies of the Mage that cast it. These copies have their own health and mana pools, and act independently of you, like three like-minded pets set to "aggressive." The copies I was summoning would alternate between casting three simultaneous Fire Blasts and three simultaneous Frostbolts. These spells do more-or-less normal damage. The Fire Blasts were hitting for around 2,000 damage each, and the Frostbolts were hitting for slightly less, around 1,500.
I summoned them the first time in range of three level 70ish mobs. The copies immediately began attacking, one shotting two of the mobs before I even realized what was happening. I began casting at the third a second later, but it was dead before the cast went off. I then moved within range of the next mob and began casting a Frostfire Bolt at it. The copies followed suit, winding up three Frostbolts simultaneously. Their spells landed just after mine, and the level 71 mob died before it had even begun to move toward me. After thirty seconds, my copies died automatically, leaving three corpses that looked exactly like me lying at my feet.
At my computer, I burst into song, and lost control of my bowels.