What does the ability UNBURDEN do?

Question

And which pokemon has it?

Answer 1

See this: http://pokemondb.net/ability/unburden

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

Comments

It was right, not wrong.

Answer 2

I don't know what pokemaster was thinking, but that is wrong again. If you have an item and it is taken from you, you will have double speed. If you take and item with a move your speed will go back to normal. It says so in my guide.

EDIT: I just realized that swampert was right, but pokemaster forgot that you can lose items by moves like bug bite.

Comments

Yes, technically it's when you have a held item then it disappears - either from being used (like a berry) or being taken from you (like Bug Bite) or another way like losing it from Knock-Off.