Speed is doubled on held item loss; boost is lost if it switches, gets new item/Ability.
Pokémon with Unburden
Hitmonlee
Treecko
Grovyle
Sceptile
Drifloon
DrifblimUnburden
Brilliant Diamond & Shining Pearl
Brilliant Diamond & Shining PearlShowing Brilliant Diamond & Shining Pearl. Items may require trading, an event, or downloadable content.
HitmonleeTreeckoGrovyleSceptileDrifloonDrifblimSources: PokéAPI, PKHeX game records, Pokémon Showdown and Serebii.