Boomerang Bro

Boomerang Bros. are a type of Koopa that, like the Hammer Bros., specialize in the use of a certain item as a weapon. Instead of throwing Hammers like the Hammer Bros., Boomerang Bros. use Boomerangs. Also, unlike their more common cousins, Boomerang Bros. are rarely seen in any Mario games at all.

Super Mario Bros. 3
Boomerang Bros. debuted in Super Mario Bros. 3 as somewhat common enemies found primarily in Desert Land. They would attack Mario or Luigi by throwing multiple boomerangs which would circle back if they missed. In order to defeat a Boomerang Bro., Mario or Luigi would need to Jump on them or throw something at it, such as a Fireball or Shell. If one of the brothers can get close enough, the creature can also be defeated by Raccoon Mario's tail.

In Dark Land, Boomerang Bros. also appear as the captains of Bowser's tank and ship forces.

New Super Mario Bros.
In New Super Mario Bros., Boomerang Bros. appear as rare enemies, appearing only once in one level of World 2 - Rich'n'Rich Desert, twice in one level of World 7 - Fall'en'dye Clouds, and twice in one level of World Eight - Bowser's Kingdom. Boomerang Bros. will, once again, attack Mario or Luigi by throwing boomerangs at them.

New Super Mario Bros. Wii
Boomerang Bros. also reappear in the sequel, New Super Mario Bros. Wii, acting and appearing in much the same way.

Yoshi's Safari
In Yoshi's Safari, Boomerang Bros. would occasionally appear as mini-bosses that would attack Mario and Yoshi by throwing boomerangs at them. These Boomerang Bros. were difficult adversaries to defeat, as they possessed a large amount of health and would run back and forth quite quickly.

Unlike other experiences with Boomerang Bros., Mario could knock away an incoming boomerang by blasting them with his Super Scope.

Super Mario Momotarō
In the short anime film, Super Mario Momotarō, a Boomerang Bro. appears as an ally of Mario, helping him rescue Princess Peach and defeat the evil ogre Bowser.

Super Mario cartoons
Boomerang Bros. appeared several times in The Adventures of Super Mario Bros. 3, serving as soldiers in Bowser's army. Through the use of their boomerangs, these goons were practical in long range attacks. Unlike in the game, it was not uncommon for Boomerang Bros. to travel together in groups.

Nintendo Comics System
A Boomerang Bro. made a relatively minor appearance in the Nintendo Comics System issue "The Kingdom Enquirer", where it attacks Mario and Toad with it's boomerangs after the two heroes exit a Warp Pipe.

Mario Superstar Baseball
In Mario Superstar Baseball, one of the alternate color schemes for the game's playable Hammer Bro. is a Boomerang Bro. that wields a large boomerang in place of a baseball bat in the same way that Hammer Bro. wields a hammer instead of a bat.

Boomerang Bro. is a power-type player in the game, and can easily obtain home runs. Beginning with this game and beyond (excluding the Paper Mario series), the Boomerang Bro. wears a blue helmet and a blue shell, similar to what the blue-shelled Koopa Troopas wore.

Mario Super Sluggers
Boomerang Bro. is also a playable character in Mario Super Sluggers. However, unlike in Mario Superstar Baseball, he has average pitching and fielding abilities, and his batting is tied with the Hammer Bro., while inferior to the Fire Bro..

Paper Mario: The Thousand Year Door
A single Boomerang Bro. named Bamma appears in Paper Mario: The Thousand-Year Door as a competitor in the Glitz Pit alongside Hammer Bro. Hamma Jamma and Fire Bro. Flare. He sports a silver shell and helmet, and his boomerang bears a single red stripe.

Similar to the Boomerang Bros. in Super Mario Bros. 3, Bamma can attack Mario and his partners by either throwing a single boomerang or multiple ones by using either his Boomerang Throw or Multiboomerang moves, respectively.

Super Paper Mario
The most recent appearance of a Boomerang Bro. was in Super Paper Mario, which featured several Boomerang Bros. that had been brainwashed by Nastasia to serve under Count Bleck.

Super Paper Mario also featured a new, shadowed sub-species of Boomerang Bro. known as a Dark Boomerang Bro..

Mario & Luigi: Superstar Saga
In Mario & Luigi: Superstar Saga, Boomerang Bros. appear with the most drastic changes thus seen. They are extremely thin, tall sunglasses-wearing creatures with sprouts growing from their heads. These sprouts and divergent appearance suggests they are the Troopea-equivalent Boomerang Bro. rather than the Koopa-derived more common variant. Despite these differences, this enemy shares the same name.

In the game, they only inhabit the Gwarhar Lagoon. In battle, Boomerang Bros. would throw their trademark boomerangs, which Mario and Luigi could Jump to avoid once on the boomerang's primary throw, and then again on it's return.

Trivia

 * Prior to the official debut of the Boomerang Bros. in Super Mario Bros. 3, The Super Mario Bros. Super Show! episode "Crocodile Mario" featured standard Koopa Troopas that attacked using Boomerangs.