Unburden is an ability introduced in Generation IV. So far, 1 Pokémon has this ability.
Unburden doubles the Pokémon's Speed stat when the Pokémon's held item is lost or consumed. If there is no held item to begin with, or if a held item is traded for another, Unburden will not be activated. This boost is lost if the Pokémon is switched out.
Outside of battle
Unburden has no effect outside of battle.
Pokémon with Unburden