Redoctane.com has all kinds of bundles for the DS game including a 2 player bundle...all pre-order of course, but if you're looking for a couple extras they are throwing in headsets and keychains.
Gets the snake hair and everything and then turns any enemies into stone. Would have to use it strategically so as not to block your path with the statues.
A Tsunami mushroom might be pretty cool. Gives new meaning to wipe out the competition...lol. It would wash away all the enemies and possibly as a side effect erode some of the environment.