Multitype

Multitype is the signature ability of Arceus, the mythical creator deity of the Pokemon universe, introduced in Generation IV. It changes Arceus's type to match the elemental Plate item it holds -- Flame Plate makes it Fire-type, Splash Plate makes it Water-type, and so on for all 18 types. Without a Plate, Arceus remains Normal-type.

Beyond the type change, Multitype provides comprehensive item protection. Arceus's held item -- whether it is a Plate or not -- cannot be removed by Knock Off, stolen by Thief or Covet, or swapped by Trick or Switcheroo. These moves still deal their damage but fail to affect the item. In Generation VII, Multitype was updated to also respond to type-specific Z-Crystals, allowing Arceus to change form through those items as well.

Multitype cannot be copied by Trace, suppressed by Gastro Acid, or overwritten by abilities like Mummy or Worry Seed. This makes Arceus's type change permanent and unbreakable as long as the Plate is held. In competitive formats where Arceus is legal (primarily Anything Goes and Ubers), Multitype's versatility allows Arceus to fill virtually any team role -- from a bulky support with Will-O-Wisp to an offensive Swords Dance sweeper -- simply by changing its Plate.