Bullet Bill

Super Mario Bullet was a minor item and murder weapon that only appeared in Super Mario. Bullet Bill had a minor part in the episode where it appeared from nowhere making Mario lose a life when he was getting angry in front of Orange's puns after Mario was shrunk by a Koopa Shell that Orange burped out when he trying to resuce Princess Peach.

Trivia

 * Bullet Bill is the exact same character who appears in the Mario video game series.
 * His sprite, alongside the sprites for Peach and Toad, were from the 1991 Super Nintendo Entertainment System game, Super Mario All-Stars, unlike Mario and the Koopa Shell, with sprites used from Super Mario World.
 * Orange and Bullet Bill were the same in toughness, as Bullet Bills are immune to fireballs in the series, same thing with Orange when Mario shot a fireball at him.
 * It is unknown how the Bullet Bill was shot, as Bullet Bills are normally shot from Bill Blasters. This could be a reference to the fact that Bullet Bills are also shot offscreen.