We've seen footage of Noby Noby Boy's multiplayer mode before, but it didn't really explain anything. Just showed some Noby's wriggling around. So creator Keita Takehashi has stepped up with a few more details.
Apparently what each player eats has a different effect on how the game goes down. For example, Takehashi says that if player 1's head eats player 2's butt, you'll end up with a single Noby Noby Boy that's controlled by two people. One moving the head, the other, its rear.
Here's an example. Cruisey.