Magician

Introduced in Generation VI, Magician steals the target's held item whenever the Pokemon lands a damaging move. The stolen item is transferred directly to the Magician user, who must not already be holding an item for the theft to occur. Any damaging move triggers the effect -- physical, special, single-target, or spread.

In competitive play, Magician can disrupt opponents by removing critical items like Leftovers, Choice Scarves, or Eviolite. The stolen item becomes immediately usable on subsequent turns. However, the requirement of having no held item significantly limits practical application -- going into battle without an item puts the user at a disadvantage before it can steal one.

Found on 5 Pokemon including Delphox and Klefki, Magician occupies a niche role. Some strategies involve using Magician after consuming a Berry to then steal the opponent's item, but this requires specific setup that more straightforward abilities do not.