I wasn't expecting too much from the Noby Noby Boy multiplayer update and was really surprised to see that much added to the game.
Of course there is offline multiplayer for up to four people, but there are also different BGMs for different maps and best of all there is an announcer voice (called Fart Boy on the official page!) telling you what you poop out of your rear end in Japanese.
Finally there are also different designs for the BOY house hair.
If you have NOBY NOBY BOY go and get the update. If you don't have NOBY NOBY BOY get it!
EDIT: You can choose your music via left stick to the left and select. You can also adjust the fart volume there.