You may or may not have discovered this, but if you haven't... When you're playing Super Mario Galaxy and you're not alone, have that someone else point the other controller at the tv. They can pick up star bits and shoot them for you. They can also freeze things like rocks, mushrooms and bullets by putting their star on them. Freezing one rock and holding it until another one hits it causes them both to explode into a shit load of new star bits.