Instructions
Travel to Route 218 or Route 222 in "Pokemon Diamond."
Search the tall grass until you find a Mr. Mime. You have a 15 percent chance of meeting one.
Weaken Mr. Mime. He is weak to ghost attacks and dark attacks. On Route 218, Mr. Mime is around level 30, while on Route 222, he is around level 40.
Capture Mr. Mime with a Pokeball.
Go to a Pokemon Center. Head downstairs to the trading center.
Start "Pokemon Pearl" in another Nintendo DS.
Go to a Pokemon Center in "Pokemon Pearl" and go downstairs to the trading area.
Talk to the lady at the desk in both games to open up the trade.
Select Mr. Mime from "Pokemon Diamond," and choose a random Pokemon from "Pokemon Pearl."
Accept the trade in each game and the Pokemon will transfer.