He uses the box to hide/disguise himself in certain parts of the games. Often, it'll result in funny animations from the guard who finds him, or a prompt beatdown from reinforcements.
Hopefully they'll add much more characters as the year goes by. I'm actually surprised the Nintendog powerup clogs up the screen with a happy puppy....a Good tactic in versus mode......
Please let them put Ridley in it this time!!!!!
Since Snake's in there, why not put Sonic in as well? How about Megaman? Hopefully more crossovers are on the way!