Bullet Bills are recurring enemies in the Mario series. They are black bullet-like enemies, commonly depicted as either having small arms or fanged grins adorning their faces, rarely having both. Bullet Bills are fired by cannons known as Bill Blasters, although some games have them fired by other sources such as Snifits and generic cannons, while some games simply have them coming out of nowhere.
Bullet Bills commonly appear as obstacles in games, attacking by either flying forward after being shot or actively seeking out a target, either smashing into a them and continuing on their way or exploding on contact, as most recent games portray them as doing. Spin-off games, such installments of the Mario Party series and Mario Kart DS feature Bullet Bills as items which can be used plow into and injure opponent characters. Perhaps due to the name and nature of the enemy, Bullet Bills only appear in two episodes of DIC Entertainment's Super Mario cartoons, but are featured with much more prominence in literature such as comics and books. The live-action Super Mario Bros. movie feature miniaturized Bullet Bills, though not named as such, as the power source of the "Thwomp Stomper" boots; a neon sign advertising a bar named "Bullet Bills" can also be seen throughout the film.
Banzai Bills are a common and much larger subspecies of Bullet Bills. They are found in Super Mario World, Super Mario Galaxy, and New Super Mario Bros. They only fly straight and are much slower. They are also the only bullet bills with mouths. They also appear in Super Smash Bros. Melee in the adventure mode and Super Smash Bros. Brawl as a trophy and enemies in the Subspace Emissary
In the games Mario Kart DS, Mario Kart Wii and Mario Kart 7 the player can collect Bullet Bills as items. Upon using the item, the user will transform into a near (if not completely) invincible Bullet Bill and rocket down the track on Auto-Pilot for a few seconds, knocking over any enemies and players in the way and stripping players of their items, similar to the Chain Chomp from Mario Kart: Double Dash!!. The Bullet Bill can only be received by the drivers on sixth to eight place (sixth to twelfth in the case of Mario Kart Wii). However, this item can sometimes be a curse. When on the trickier, narrower courses, these can sometimes lead racers up to a sharp turn or obstacle on the track and then end, possibly causing the kart to fall off the track and lose some of the spots gained using that item but the perks overshadow the cons of using it. Players can avoid this item if they are far ahead of the person using it, invincible, or out of the flight path. This is also one of four items which can be used to dodge a Blue Shell (the others being a Mushroom, a Starman, and Mario Kart Wii's Mega Mushroom).
Bullet Bills also appear as obstacles on the Airship Fortress track, which appear in Mario Kart DS and reappears as a Retro Course in Mario Kart 7.