Boom Boom

Boom Boom (sometimes stylized as BOOM-BOOM) is a henchman of Bowser who first debuted in Super Mario Bros. 3. He is a "mini-boss" that Mario or Luigi fights in each fortress, before the player fights a Koopaling in an airship.

''Super Mario Bros. 3
First appearing in Super Mario Bros. 3, Boom Boom has joined Bowser and the Koopalings for invading the Mushroom World's seven kingdom. Since the Koopalings rules over the seven kingdoms and Bowser kidnaps Princess Toadstool when Mario left, Boom Boom appears in many fortresses fighting Mario and Luigi to prevent them for going any further closer to the Koopalings. But in Dark Land, Boom Boom is found in airships, battleships and tanks as well.

To defeat Boom Boom, Mario has to jump on his head three times to eliminate him, or hit him with fireballs or hammers if he possessed the Fire Mario or Hammer Mario power-ups, respectively. Boom Boom can also temporarily crouch down and reveal his spikes, which, if jumped on, would result in Mario powering down or losing a life. Boom Boom would begin by simply walking left and right towards Mario. After being hit, he would start to charge, jump, and in some cases, fly with his winged arms. After being defeated, he will release a ? Ball, which destroys the fortress Boom Boom was in. Which is what happening everytime when Mario and Luigi defeat him.

Whether Boom Boom is a true species or just a recurring single character is unclear, but there are at least two Boom Booms in existence, as a few extra levels in Super Mario Advance 4: Super Mario Bros. 3 will pit two Boom Booms against Mario simultaneously. However, Boom Boom may be only one character, with clones of himself. This is possible because the manual refers to Boom Boom as singular in the description: "Boom Boom, the faithful servant of Bowser."

''Super Mario 3D
After several years absence, Boom Boom is expected to appear in the game, Super Mario 3D. Boom Boom has now a red spikeless shell and attacks spinning wildly with his arms and fists to hurt Mario to the point he becomes dizzy and vulnerable by doing so. When hit he can also attack retreating into his shell and then move about at random directions, in a similar fashion to the Koopalings when they are hit by Mario. Just like in the old times, he is (currently) found in an airship level, which is the World 2's fifth level.

''The Adventures of Super Mario Bros. 3
At least one Boom Boom appeared in Mario cartoon series The Adventures of Super Mario Bros. 3, where he was nothing more than a silent power house. Much like in the game, only one Boom Boom was ever seen at any given time.

Super Mario Bros. film
In the Super Mario Bros. film, there was a bar called the "Boom Boom Bar," which was featured with some prominence in the movie.

Nintendo Adventures
In the book Koopa Capers from the Nintendo Adventure Books series, there is an item called Boom Boom's Socks, which is a reference to Boom Boom.

Trivia

 * In Super Paper Mario, one of the Sammer Guys that can be fought is named Flailing Boom Boom, which is an apparent reference to Boom Boom and how he would flail his arms around in battle.