A Plate (Japanese: プレートPlate) is a type of held item introduced in Generation IV, primarily for use in changing Arceus's elemental type and form to the corresponding type of Plate. However, it will also increase the attack power of moves of the Plate's type used by any Pokémon holding it by 20%. The Plates also change the type of Judgment, and due to this, Judgment will always have effectively 120 power. There is a Plate available for every elemental type except Normal, and while there exists a Template:Type2 Arceus, there is no associated ??? Plate, meaning there are 16 Plates in total.
The 16 Plates are spread far and wide across Sinnoh, and additional ones can also be dug up in the Underground. The captain of the S.S. Aqua will also give one away at random each time the ship sails. What follows is a list of what effect a Plate has when held and where they can be found in Generation IV, besides in the Underground.
Inside Oreburgh Gate, use Rock Smash to go north up the path, then follow around and take the stairs to the basement. Surf to the far left of the cave and use Strength to get to the Poké Ball. The Underground
Secondary effect:
Makes Arceus a Ground-type Pokémon and makes Judgment a Ground-type move.
A stone tablet that boosts the power of Electric-type moves.
Engravings
Each Plate has a different engraving which reveals part of the myth of the creation of the Pokémon universe. No engraving is tied to a specific Plate; they will appear each one at a time depending on how many Plates the player has found so far, with the ninth Plate found using the same engraving as the first. In Platinum, after talking to the Hiker on the second floor of the Canalave Library, a book on the second floor with the engravings written in it will be left by the hiker the player met in Oreburgh Mine.
"When the universe was created, its shards became this Plate."
The Plates appeared again in Arceus and the Jewel of Life, where Arceus used them to change its type, and almost died when it lost the Plates after having destroyed a meteor. Damos found one the 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 Michina Town flourish.
While the presence of hidden Plates can be determined with the Pokétch application Dowsing Machine, their exact location is difficult to ascertain. The Plate's exact location must be touched on the Dowsing Machine in order for it to be revealed.
Plates may have some relation to shards, which are described as pieces of ancient tools. Their underground sprites likewise indicate that they are merely broken parts of plates.
Although there is not a plate to change Arceus's type to ???-type, in the "After You Complete Diamond and Pearl" guide, in the Underground section, in the list of plates it includes "Magical Plate". The reason for this is unknown.