Change your preferences here.
On switch-in, the opponent's held item is displayed. In multi battles, it randomly selects an opponent, and does not tell you which opponent was selected. Frisk will immediately activate whenever the ability is acquired, such as through Skill Swap or Role Play.
This ability can be a nice benefit, since it uncovers the foe's held item, putting you one step ahead of your opponent, as you can accurately predict the opponent's set from the item it is holding before it has even had a chance to move. For example, Rotom-W holding a Choice item will likely use Trick on you rather than a status move, or Latios holding Choice Specs will likely have Draco Meteor. However, the ability's distribution is rather disappointing, as the ability is more or less limited to poor Pokemon such as Stantler and Banette, and even those Pokemon have better abilities to use. The only halfway decent Pokemon to receive the move is Yanmega, through the Dream World, who already has two far better abilities to make use of instead.
Found in Dream World