Unburden

Doubles Speed upon using or losing a held item.

Full effect

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.

In game description

Boosts the Speed stat if the Pokémon's held item is used or lost.

Pokemon with Unburden

#0106

Hitmonlee hidden #0252

Treecko hidden #0253

Grovyle hidden #0254

Sceptile hidden #0425

Drifloon #0426

Drifblim #0509

Purrloin #0510

Liepard #0617

Accelgor hidden #0684

Swirlix hidden #0685

Slurpuff hidden #0701

Hawlucha #0827

Nickit #0828

Thievul #0903

Sneasler #0944

Shroodle #0945

Grafaiai

Using Unburden in Cobblemon

Abilities are passive and always active, so Unburden costs you nothing to run. If it is marked hidden on a species above, expect it to be harder to obtain: servers differ in whether hidden abilities come from breeding, an Ability Patch, or events.

See the Pokedex for which abilities each species can have, and IVs, EVs and breeding for how to actually pass one down.