Split Personality

Split Personality is a dungeon & raids achievement earned for defeating Grand Magus Telestra in The Nexus on Heroic difficulty after having killed her images within 5 seconds of the first one dying during each split.

Strategy
The major part of this achievement is damage control; all her clones need to remain near the same health to make sure they all die at the same time. This can easily be done with aoe damage or frequently switching targets.

Now the major problem with this achievement is that while casting, the clones will not die until they finish. While this isn't a big problem with short cast spells such as Polymorph, the long, channeled Blizzard spell lasts long enough to fail the achievement. Because of this, players should be ready to stun or interrupt.

One last thing to worry about is pets; they won't switch targets and thus can damage one clone faster then the others, and might even kill one early. As such, you should frequently have you pet change targets or not use a pet at all. Also, abilities such as Mirror Image or Army of the Dead should not be used, because the pets cannot be controlled.