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Whenever a Pokemon is withdrawn, either through switching or through U-turn (but not Baton Pass), if an enemy Pokemon has selected Pursuit for use, has not yet taken its turn, is not frozen, is not sleeping, and is not about to miss its turn due to Truant, then that enemy Pokemon uses Pursuit with double power on the Pokemon being withdrawn, and skips its normal turn. Otherwise, the user uses Pursuit normally on its turn against the selected target.
In Japanese Diamond / Pearl, if a Pokemon with Choice Band / Choice Scarf / Choice Specs uses Pursuit on its first turn out, and the target switches out and is KOed, the Pokemon using Pursuit can select a new move. In English Diamond / Pearl and Platinum, the Pursuit user is locked into Pursuit.