The Mastermind of Mirage Pokémon (戦慄のミラージュポケモン, Senritsu no Mirāju Pokemon?, lit. "The Terrifying Mirage Pokémon") is a special hour-long episode of the Pokémon anime series created for the tenth anniversary of the franchise. This special premiered on Kids' WB! on April 29, 2006. It became available on DVD in the United States on September 19, 2006 as a special feature on the 2-disc Pokémon: Lucario and the Mystery of Mew release. In Japan the special was available for download as 戦慄のミラージュポケモン on the official site from October 13-October 31, 2006.

This special marked the first time English-language production was handled by Pokémon USA and TAJ Productions rather than 4Kids Entertainment, who were responsible for all Pokémon licensing except video games, and the trading card game outside of Asia from 1998 until 2005. As a result of this change, the English-language version of the special featured an all-new voice cast, replacing the 4Kids-based actors, many of whom had worked on the show for eight years. The one exception was Rodger Parsons, who returned at the narrator.

This change has caused controversy among some fans. It was announced at the 2006 San Diego Comic-Con that the version available on DVD would be improved from that aired on TV, with dialogue being re-recorded after the new voice cast were more used to their roles and after Ash was given another new voice actor Sarah Natochenny.

Source: Wikipedia