This is a glitch in Super Mario 64 that works like the Big Bob-omb Glitch. What you do is grab the small box near the beginning of Bob-omb Battlefield. Carry it up the bridge, and throw it at a steep cliff (the one near the small koopa works well, assuming you are on a star after Koopa the Quick and the small koopa is there). Here is the frustrating part. Dive at the box and catch it just after it collides with the wall, and Mario will do his carrying animation, but will be holding nothing. Run across the bridge next to the Chain Chomp, and the nothingness you are holding turns into a goomba! It may also turn into other things as you run around the level.
Why it works Edit
Similar to in Big Bob-omb Glitch, you are catching the box in the point in its animation after it has exploded but before it releases its coins. This makes you do your carrying animation. Since you're supposed to have something in your hands with that animation, the game starts sticking random objects in your hands.
This glitch was discovered on Google Video.