Boomerang

Boomerangs are a type of weapon that have made numerous appearances throughout the Mario series. When thrown, a boomerang will fly forward, harming any foes who happen to be in its path, then circle back to the user. They are the weapon of choice of the Boomerang Bros., but can also be used by Mario, Luigi, Princess Peach, Toad, and Rosalina upon grabbing a Boomerang Flower.

Super Mario Advance 4: Super Mario Bros. 3
A special blue Boomerang makes an appearance in some of the World-e levels of Super Mario Advance 4: Super Mario Bros. 3. When thrown, this Boomerang defeats most enemies it hits. It briefly flies forward before turning around, though it only does so once; as such, Mario must catch it if he hopes to re-use it. However, it disappears upon level completion, much like a Goomba's Shoe.

Certain Boomerang Bros. are also shown using these boomerangs in Slidin' the Slopes, Bowser's Last Stand, and Bowser's Airship 2, and if they are defeated while one of their boomerangs is out, it drops for the player's use.

There is also an e-Reader card released only in Japan that uploads this boomerang to the player's inventory, allowing Mario to use it in any stage.

Super Smash Bros. for Nintendo 3DS / Wii U
Boomerangs appear as a new item in Super Smash Bros. for Nintendo 3DS / Wii U. The boomerang that appears in these games is said to be and designed after the one used by Boomerang Mario in Super Mario 3D Land. They function like standard boomerangs in that they are thrown to attack opponents and return to the thrower, though for every time the player catches it the boomerang's attack becomes stronger. Other players can catch the boomerang after it is thrown, however.

Super Smash Bros. for Nintendo 3DS / Wii U Trophy information
Blue indicates exclusive to the Wii U version.