Magician is a hidden ability found in a few animals.
In Battle Use
This ability only activates if the animal with the Magician ability is not holding an item and if the opponent is holding an item. When the Magician ability animal attacks its foe, it will promptly steal the item held by its opponent (much like the Thief move).
This ability likely evolved from scavenger-like animals. The quick theft of another animal's item is possibly associated to how animals would steal prey from other predators.