Depiction in the seriesThe Mirror Pool is a small pond of water located in an underground cavern in the Everfree Forest, connected to the surface via tunnel. The cavern walls surrounding the pool are covered in luminescent flowers and mushrooms.
In the season three episode Too Many Pinkie Pies, Pinkie Pie struggles to spend quality time with all of her friends at once. When Twilight Sparkle tells her the only way to accomplish this is if there are more of her to go around, Pinkie recalls the "legend of the Mirror Pool" told to her by her Nana Pinkie, which includes these rhymes:
- "Where the brambles are thickest, there you will find
A pond beyond the most twisted of vines."
"And into her own reflection she stared,
Yearning for one whose reflection she shared,
And solemnly sweared not to be scared
At the prospect of being doubly mared."
- — The Legend of the Mirror Pool
Venturing into the Everfree Forest, Pinkie Pie stumbles through some brambles and vines and finds herself in the Mirror Pool's underground cavern. By staring into her reflection and reciting the last part of the legend, she activates the pool's magic, and her reflection turns into a clone that climbs out of the water. This duplicate Pinkie is notably single-minded and obsessed with fun, repeatedly chanting the word "Fun!" in her speech, and she constantly gets the names of Pinkie Pie's friends wrong.Pinkie Pie creates one clone of herself at first, but she later returns with the clone to create two more. The three Pinkie clones then create even more clones, making a minimum total of thirty-three. Pinkie Pie's duplicates cause general mayhem around Ponyville, such as ruining Applejack's barn-raising at Sweet Apple Acres and disturbing Rainbow Dash's nap.
Twilight reads about the Mirror Pool, referring to it as the "Mirror Pond", in a hidden book in her library and learns of a spell to return the clones to the pool. Through a test to find the real Pinkie Pie, Twilight has the Pinkie clones watch paint dry and magically zaps any that gets distracted back to the Mirror Pool. After the real Pinkie passes the test, Twilight and Big McIntosh seal the entrance to the Mirror Pool's underground cavern with a boulder.
The Mirror Pool briefly appears again in Pinkie Pie's dream in the season five episode Do Princesses Dream of Magic Sheep? In the season six episode The Saddle Row Review, Pinkie Pie alludes to her previous use of the pool. In the season seven episode Uncommon Bond, Starlight Glimmer breaks the seal on the Mirror Pool's entrance in order to show Sunburst, and Maud Pie's home cave is revealed to be adjacent to it. In that episode as well, Boulder is duplicated (offscreen) through use of the pool.
The Mirror Pool is mentioned in narration within chapter 1 of Pinkie Pie and the Rockin' Ponypalooza Party!, "Welcome, Spring-Sproing Springtime", and chapter 8 of Rarity and the Curious Case of Charity, "A Big Splash".
In series 2 of Enterplay's trading cards, card #42 of Tom mentions him "finding work as a guard—no swimming allowed in the Mirror Pool, or else you'll answer to Tom!", and card #50 of the Mirror Pool gives it the description "Venture into the Everfree Forest where the brambles are thickest, and there, beyond the most twisted of vines, you will discover the Mirror Pool. Stare into your own reflection and recite the magical words of legend, and you will soon be doubled into your own pony clone! Just be careful what you wish for, as this duplicate will be obsessed with whatever you were thinking about when you peered into the pool. And as soon as you turn your back, she might duplicate herself over and over and over and over and over and over and over and over and over..."
In the High Magic expansion set of Enterplay's collectible card game, the Mirror Pool is depicted on card #88 R, Dip in the Pool.