It's a klaw cancel it seems. It does foward b and gets a jump somehow after touching the ground (notice when trying near sheik, he klaws her). My gawd that is sick. Aerial and klaw cancel nonstop, that is gonna make a real good airborne technique for bowser (notice how every little thing can help a slow characer like him lol, that is Brawl's answer to waveland guys).
EDIT: what the hell i'm just realizing the usefulness of this: since there is no real l-cancel (at least you can't time your fall the way you want) this is just a perfect attack for landing (since others can't perform falling aerials that good). Lol Bowser fo' top tier.