Banzai Bill

Banzai Bills are an extremely large variety of Bullet Bills that first appeared in Super Mario World. These huge bullets are black and have shark-like smiles. In the game, Banzai Bills are fired off-screen and travel slowly towards Mario. Although they seem impossible to defeat, Banzai Bills are not very strong. In fact, they can be destroyed by simply jumping on top of them (just like regular Bullet Bills). Fireballs are ineffective against Banzai Bills.

Banzai Bills reappear in the New Super Mario Bros. These Banzai Bills look like their Super Mario World counterparts, except that they have red shadow under their eyes to make them look more intimidating. In this game Banzai Bills are fired from huge Banzai Bill Blasters (unlike Super Mario World, where they are fired from an unknown source). Additionally, these Banzai Bills travel very slowly, twirling in the air. Again, a simple jump is enough to defeat these massive shells.

Other Appearances
Banzai Bills are a major threat in Super Smash Bros. Melee. At the Princess Peach's Castle stage, Banzai Bills will randomly enter the battle, colliding into the castle. Once burrowed into the wall, a Banzai Bill will detonate, causing massive damage to anyone caught in its explosion. If there is an unpressed button in reach of the explosion, it'll cause it to be pressed

Also in Super Smash Bros. Melee, a Banzai Bill (as it looks like in Super Mario World) appears in the background of the Yoshi's Island stage.