Where is trash and sand cloak Burmy in Pokemon Pearl ?
To get trash cloak, level up Burmy in a building. To get Sandy Cloak, level up Burmy in a cave.
Source:http://www.gamefaqs.com/ds/925601-pokemon-diamond-version/answers?qid=9420
(just had to google it......)
Burmy's form changes after each battle, depending on the environment it just battled in
So you have to battle in buildings to get Thrash, Caves/Sand to get Sandy and Grass to get Plant
Source