From Bulbapedia, the community-driven Pokémon encyclopedia.
Poké Transfer (Japanese: ポケシフター PokéShifter) is a feature in the Generation V games Pokémon Black and White and Pokémon Black and White 2. It is located in the Poké Transfer Lab on Route 15.
The Poké Transfer is a feature that allows Pokémon from any Generation IV game to be transferred to Pokémon Black and White, similar to Generation IV's Pal Park. It can be visited after the main storyline of the games has been completed and the player has obtained the National Pokédex.
By using the Nintendo DS's Download Play, a player can send six Pokémon from a Generation IV game to Black and White. The player will then participate in a mini-game in which they must capture the Pokémon using a bow that shoots special Poké Balls. There is a time limit, and if all six Pokémon are not captured within the time limit, the Pokémon not captured will be sent back to the Generation IV game, while those that are caught will be sent to the Black or White game, allowing less than six Pokémon to be sent at a time. The player has no limits on how many Pokémon they can transfer a day. Like Pal Park, Pokémon sent over cannot be returned to any Generation IV game. Pokémon are not allowed to have held items, or know any HM moves. Any Pokémon can be transferred over, except the Spiky-eared Pichu and Eggs. Attempting to transfer the Spiky-eared Pichu will yield the message "Oh! This Pichu needs to stay where it is. It appears to have traveled through time. It has been affected by traveling so far through time with Celebi. It'll be risky to transfer it, so it's best for Pichu to stay where it is."
In the mini-game, there are several rows of bushes that the Pokémon hide behind, sticking their heads out from time to time, or jumping from bush to bush at varying speeds. The only time that they can be caught is when their head/body is not covered by a bush. To help with the catching of Pokémon, near the end of the time limit a pink cloud of Sleep Powder will float across the screen, which will put all Pokémon to sleep. While they are asleep, the Pokémon can be hit regardless of where they are, and have their position shown by sleeping "zzz"s. It is possible for a Pokémon to have jumped off-screen when they are put to sleep; in that case, they won't be possible to hit until they wake up and come back on-screen.
When a Pokémon is transferred, its location becomes simply the name of the region it was caught rather than the exact location it was caught. A Pokémon caught in HeartGold or SoulSilver will have its location listed as Johto, regardless of if it was caught in Kanto, the Sinjoh Ruins, or the Pokéwalker. A Pokémon originally caught in a Generation III game will have the text "after a long travel through time" added to the end of its location. In addition, the level obtained at is changed to the level arrived at, and the date obtained becomes the date it was transferred to the Generation V game.
Like Pal Park, Poké Transfer reads only the data of the game the Pokémon was originally generated in, rather than its in-game met-at location. This sets any Pokémon created in FireRed or LeafGreen to Kanto; HeartGold or SoulSilver to Johto; Ruby, Sapphire, or Emerald to Hoenn; and Diamond, Pearl, or Platinum to Sinnoh. A Pokémon whose Egg is created in a game based in one region and traded to another region before it was hatched will display the name of the region it was generated in, rather than the one it was hatched in, meaning a Pokémon generated in Platinum but hatched in SoulSilver would have the OT and ID of SoulSilver's player but list that it was met in Sinnoh.
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