The Mirror Pool has been a lost artifact for centuries. That is, until Pinkie Pie decided to misuse it.

Twilight Sparkle falls in to said pool while researching it. Instead of making a clone, she finds that the Mirror Pool is more than a cloning pool, but a portal to a twisted reflection of Equestria.

She manages to escape, but soon one by one her friends start to disappear, taken by what witnesses claim was her. Twilight must travel back to the mirror world, but things are not as simple as they seem when the mirror world reflects the inner selves of the ponies that fall in...