Plate Types
You can find a plate for each elemental type with the exception of Normal type. The names of each plate reference their related type: for example, the Draco Plate is related to the Dragon type, while the Meadow Plate is related to the Grass type.
Normal Pokemon
When a normal Pokemon holds a plate, the attack power of moves belonging to that plate's type is increased by 20 percent. For example, a Pikachu using Thunder while holding a Zap Plate will have an attack power of 144 rather than 120.
Arceus
When the legendary Pokemon Arceus is holding a plate, its type and form will change to match the elemental type of the plate. Additionally, Arceus' signature move, Judgment, will also change type to match the elemental type of the plate.
Considerations
Equipping your Pokemon with a specific plate can be quite useful when dealing with an opponent who uses Pokemon that are weak to a specific elemental type; through the use of plates, your Pokemon will deal more damage and therefore you will defeat the opponent faster. Similarly, if using Arceus, plates will allow you to tailor Arceus' signature move to your opponent's weakness.