The winged shell is the new spikey blue shell. It flies over the course, so that it's not restrained by walls.
And I don't know what the whole deal is behind item stealing, but if you hit another kart hard enough to knock the back player over, he/she will drop any items in order to get a better grip on the kart. The items fall to the track, and are effective there. Things like shells and banana peels become obstacles, and things like stars and mushrooms become instant powerups.
Go Moon!