Multitype changes an Arceus holding this item to its Electric-type form. From Generation V onward, item-manipulating effects (such as Trick and Fling) cannot give Arceus a Plate or remove a Plate from Arceus. (In Generation IV, item-manipulating effects cannot affect Pokémon with Multitype.)
The Zap Plate, alongside the other 15 Plates at the time, appeared in Arceus and the Jewel of Life, where Arceus used them to change its type, and almost died when it lost all of the Plates after having destroyed a meteor that endangered the land that would become Michina Town. Damos found one of these lost Plates and returned it to Arceus, giving it the strength to recall the other 15 Plates. That act earned its trust and prompted it to detach the Earth Plate, Splash Plate, Meadow Plate, Zap Plate, and Draco Plate in the form of the Jewel of Life so Damos could make the land flourish. The Zap Plate was included in the Jewel of Life to bind the energies of the Earth, Splash, and Meadow Plates together.