Unburden

Unburden is an ability in the Pokémon series that significantly enhances a Pokémon's speed in battle. When a Pokémon with Unburden loses or uses its held item, its Speed stat is doubled. This dramatic increase in speed can be a game-changer, allowing the Pokémon to outspeed opponents it normally could not.

Effects

Triggering the Ability: Unburden activates when the holder's item is consumed or removed. This includes using a consumable item like a Berry, being hit by moves that remove items (such as Knock Off), or using moves like Acrobatics that depend on not holding an item.
Speed Boost: Once Unburden is activated, the Pokémon's Speed stat is doubled. This effect remains until the Pokémon switches out or faints, persisting for the entire duration that it's on the field.
Stacking: The Speed boost from Unburden can stack with other Speed-boosting effects,

Effects

When this Pokémon uses or loses its held item, its Speed is doubled. If it gains another item or leaves battle, this bonus is lost. This includes when the Pokémon drops its item because of knock off. This bonus does not count as a stat modifier. There is no notification when this ability takes effect.

Flavor Texts

diamond-pearl: Raises Speed if a held item is used.
platinum: Raises Speed if a held item is used.
heartgold-soulsilver: Raises Speed if a held item is used.
black-white: Raises Speed if a held item is used.
black-2-white-2: Raises Speed if a held item is used.
x-y: Boosts the Speed stat if its held item is used or lost.
omega-ruby-alpha-sapphire: Boosts the Speed stat if its held item is used or lost.
sun-moon: Boosts the Speed stat if the Pokémon’s held item is used or lost.
ultra-sun-ultra-moon: Boosts the Speed stat if the Pokémon’s held item is used or lost.
lets-go-pikachu-lets-go-eevee: Boosts the Speed stat if the Pokémon’s held item is used or lost.
sword-shield: Boosts the Speed stat if the Pokémon’s held item is used or lost.
scarlet-violet: Boosts the Speed stat if the Pokémon's held item is used or lost.