Now that LittleBigPlanet Karting's launch date nears, the antagonists have been announced. The Hoard are out to steal all of the prizes. They come in swarms just to hoard the prizes.
PlayStation Blog describes The Hoard:
They essentially embody the antithesis of Creative Sackartistry. So, the LittleBigPlanet Karting adventure begins with a very distraught Sackboy – distraught because he is forced to watch The Hoard fly past him and steal prizes at speeds greater than he can possibly match!
Here are some images of them.