Reveal Glass

The Reveal Glass (Japanese: うつしかがみ Utsushi Kagami, literally meaning; "Reflecting Mirror") is a exclusive key item only for the Pokémon Black 2 and Pokémon White 2 Versions. After that the player transfer his/her Landorus from the Pokémon Dream Radar to the game and bring him in his Therian Forme to the Abundant Shrine the player will receive the Reveal Glass which can change the form of Tornadus, Thundurus, and Landorus into their Incarnate Forme to their Therian Forme and can switch back in their Therian Forme to their Incarnate Forme.

In the anime
The Reveal Glass was first seen in Meloetta and the Undersea Temple! in the hands of Giovanni. Giovanni used this item to transform the Forces of Nature into their Therian Formes after successfully summoning them using Meloetta's song to open up a seal in the Abyssal Ruins during Operation Tempest. Giovanni looks into the Reveal Glass, opening up the top of the temple. He orders the glass to summon Landorus, Thundurus, and Tornadus.

Trivia

 * The Reveal Glass may be based on the Demon Detecting Mirror, an item in Chinese fairy tales could reflect true identity of Yaoguai.