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.

Super Mario Bros. 3
In Super Mario Bros. 3, Boomerang Bros. appear as somewhat common enemies, primarily in Desert Land, attacking Mario or Luigi by throwing multiple boomerangs which would circle back to the enemies if they missed the plumbers on the first pass. In order to defeat a Boomerang Bro., Mario or Luigi would need to jump on it 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 somewhat rare enemies, appearing once in one level in World 2, twice in one level in World 7, and twice in 1 level in World Eight. The Bros. will, once again, attack Mario or Luigi by throwing boomerangs at them.

New Super Mario Bros. Wii
They also reappear in the game New Super Mario Bros. Wii.

Yoshi's Safari
In Yoshi's Safari, Boomerang Bros. would occasionally appear as mini-bosses who would attack Mario and Yoshi by throwing boomerangs at them; the Boomerang Bros. of Yoshi's Safari are difficult adversaries to defeat, as they posses a large amount of health and run back and forth quite quickly. Also of note, in Yoshi's Safari, Mario could knock away an incoming boomerang by blasting them with his Super Scope.

Super Mario Amada series
In the Momotarō segment of the Super Mario Amada Series, 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. also 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 in the show.

Nintendo Comics System
A Boomerang Bro. made a relatively minor appearance in Nintendo Comics System issue "The Kingdom Enquirer", where it attacks Mario and Toad with it's boomerangs after the two 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., who 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. Unlike in Mario Superstar Baseball though, he has average pitching and fielding abilities, and his batting is tied with the Hammer Bro., while being inferior to the Fire Bro.'s batting.

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; similar to the Boomerang Bros. in Super Mario Bros. 3, Bamma will attack Mario and his partners by either throwing a single boomerang at him or multiple ones.

Super Paper Mario
The most recent appearance of Boomerang Bros. was in Super Paper Mario, which featured several Boomerang Bros. which had been brainwashed by Nastasia to serve under Count Bleck. Super Paper Mario also featured a new, shadowed sub-species of Boomerang Brothers known as Dark Boomerang Bros..

Mario & Luigi: Superstar Saga
In Mario & Luigi: Superstar Saga, Boomerang Bros. appear as extremely thin, tall sunglasses-wearing creatures with sprouts on their heads. These sprouts and divergent appearance suggests they are a subtype of Troopea rather than true relatives of the Hammer Bros. In the game, they inhabit Gwarhar Lagoon. In battle, the Bros., as usual, would throw boomerangs, which Mario and Luigi were forced to jump to dodge once on the boomerang's primary throw, and then again on it's return.

Trivia

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