A Banzai Bill Cannon is an object/enemy from the Super Mario series.
Super Mario series
Banzai Bill Cannons debut in New Super Mario Bros., where they appear only at the end of World 7-5 and World 8-1 and help the player reach the tops of the flagpoles. They appear in every other game in the New Super Mario Bros. series, including New Super Mario Bros. Wii, New Super Mario Bros. 2, New Super Mario Bros. U, New Super Luigi U, and New Super Mario Bros. U Deluxe. In New Super Mario Bros. games that use 3D models for Banzai Bill Cannons, their full model is only the visible half-portion of the cannon.
They also make an appearance in Super Mario Galaxy's final level, Bowser's Galaxy Reactor, Super Mario Galaxy 2, Super Mario 3D Land, Super Mario 3D World, Super Mario Odyssey and Super Mario 3D World + Bowser's Fury. They act the same way as they did in previous titles, albeit in a 3D space.
Banzai Bill Cannons appear as course elements in Super Mario Maker 2 in the Super Mario 3D World style, where they can be placed in the background launching Banzai Bills towards the screen.
Mario & Luigi series
Mario & Luigi: Bowser's Inside Story / Mario & Luigi: Bowser's Inside Story + Bowser Jr.'s Journey
In Mario & Luigi: Bowser's Inside Story and its remake, before Fawful took over Bowser's Castle, Private Goomp, Corporal Paraplonk, and Sergeant Guy were able to salvage a Banzai Bill Cannon, and escaped with it. Bowser later encountered the group carrying the cannon through the forest, and they told him that they were going to launch a Banzai Bill at the castle, though he then learned that they had no Banzai Bills. After Bowser recovered one from Wiggler, they launched it at the castle, though before it could make contact, Midbus had the castle float into the air, efficiently dodging the Banzai Bill.
Mario & Luigi: Dream Team
In Mario & Luigi: Dream Team, the Sergeant Guy Cannon is a Banzai Bill Cannon used in the battle against the Elite Trio. Sergeant Guy uses it in one of his attacks, taking two full turns to have it prepared. In the first turn, the Banzai Bill is manually loaded into the cannon by a few Shy Guys. On the second turn, it gets launched.
Paper Mario series
Paper Mario: Sticker Star
In Paper Mario: Sticker Star, Bowser Jr. uses a Banzai Bill Cannon aboard his airship in World 6-2. At one point to progress, Mario has to paperize the Banzai Bill Cannon scrap and turn it around, causing it to blast a hole through the ship and subsequently break down. It originally would have been a fightable enemy known as Banzai Blaster, but was cut.
Paper Mario: Color Splash
In Paper Mario: Color Splash, Banzai Bill Cannons appear in Black Bowser's Castle. They are used to fire Banzai Bills filled with black paint. When Mario blows up Bowser's black paint factory, the Cannons start firing Banzai Bills the same way they do in other games.
Puzzle & Dragons: Super Mario Bros. Edition
In Puzzle & Dragons: Super Mario Bros. Edition, a Banzai Bill Cannon appears as a ally, though under the name Banzai Bill. It is a dark/light ally with 2 star HP, 5 star ATK, and 0 star RCV. It evolves from Bullet Bill and evolves into King Bill. It has the skill armor break and the awoken skill dark boost.