Multitype changes the form and type of a Pokémon with this Ability depending on the Plate attached. The item-removing effects of Thief, Covet, Trick, Switcheroo, and Knock Off will not work on a Pokémon with Multitype, regardless of what item it is holding.
When a Pokémon transforms into Arceus, it becomes the same form and type as the target Arceus. If the transformed Pokémon is holding a Plate that is different from the target's held Plate, it then immediately changes to the form and type corresponding to that Plate; if it is not holding a Plate, it immediately changes to Normal Arceus (unless it transformed into Normal Arceus).
Role Play, Gastro Acid, and Worry Seed fail if the target has the Ability Multitype. Skill Swap fails if either Pokémon has Multitype. Multitype cannot be copied by Trace.
Generations V and VI
If a Pokémon transforms into Arceus, the Pokémon will now be in the same form as the target Arceus, regardless of its own held item.
Multitype no longer has an effect on items; instead, item-manipulating effects cannot affect Arceus if they would cause it to hold a Plate or take a Plate it already holds.
Simple Beam and Entrainment fail if the target has the Ability Multitype. Multitype cannot be replaced by Mummy.
Multitype will also change Arceus's type and form if it holds a type-specific Z-Crystal.
Multitype cannot be copied by Power of Alchemy or Receiver. Multitype cannot be suppressed by Core Enforcer.
Outside of battle
Multitype has no effect outside of battle.