Lostlorn Forest (Japanese:迷いの森Lost Forest) is a location in the Unova region. At the end of the forest you'll see a trailer with a girl in it. When you talk to her she says nothing. When you bring one of the Crown Beasts (Shiny Raikou, Entei or Suicune) to Lostlorn Forest using the Transfer Machine, the girl gets out of the trailer and lets out a cry and reveals that she is a female Zoroark, it is at Level 25 and it transforms into another Crown Beast that you didn't transfer: if you send a shiny Raikou, you'll see a normal Entei, if you send a shiny Entei, you'll see a normal Suicune, and if you send a shiny Suicune, you'll see a normal Raikou. There is no other way to get Zoroark, other than going to Gamestop during the shiny trio of Johto event, or by evolving Zorua from the Celebi event, which was also a Gamestop event.
After beating/capturing Zoroark (in Black and White), the illusion covering Lostlorn Forest is lifted, and its true form is revealed; a meadow with a few trees in the middle of it. In Black 2 and White 2, the illusion doesn't exist, and if you talk to the "hiker" in the northern part of the meadow, he will give you TM Snarl after telling you about Zoroark's Illusion ability. As he walks away, he will unveil that he is actually a Zoroark, possibly the one that guards the cave entrance to N's Castle.