Boomerang

Boomerangs are weapons carried around by the Boomerang Bros.. When thrown, a Boomerang will eventually reverse it's direction and fly back to the Boomerang Bro that threw it.

In Super Mario Advance 4: Super Mario Bros. 3, there is a special variety of blue Boomerangs that Mario can find and use, although they are very rare. The only level where Mario can find one is in the World-e level Slidin' the Slopes. Near the end is a Boomerang Bro with a blue Boomerang. If Mario defeats him, he will drop his Boomerang, which Mario can pick up and throw. If Mario fails to catch his own thrown Boomerang, he will lose it. However, since it comes at the end of the level, it will be of little use to Mario, as it disappears upon completion, much like Kuribo's Shoe.

There was also an e-Reader card released only in Japan that uploaded a Boomerang to the player's inventory. Additionally, a few other Japan-only levels featured Boomerang Bros. with blue Boomerangs.

In Mario Superstar Baseball, the Boomerang Bro player uses a Boomerang as a baseball bat.

Link and Young Link also use a Boomerang in the Super Smash Bros. series.

Appearances in Other Media
The first known appearance of Boomerangs in the Mario series was in The Super Mario Bros. Super Show! episode "Crocodile Mario". In this episode, Koopa Troopas attacked Mario and Luigi with boomerangs, which was rather fitting, due to the fact that the episode was set in the Australian-esque locale of Down Under Land. Later in the episode, Mario bent his plumber's helper into a working boomerang of his own, which he dubbed as his "plumberang".