Boomerang Bro

Boomerang Bros. are fairly common enemies in several Mario games as well as various spinoffs.

Most commonly, they throw boomerangs to attack, to avoid them, Mario has to jump over them. Also, when their boomerangs fly back to them, they can still damage Mario. The easiest way to defeat them is to throw a shell or the like to kill them. Mario can also jump on them to kill them. They appear to be related to Hammer Bros..

Paper Mario: The Thousand Year Door
Boomerang Bros only appear in the Glitz Pit in this game. A single Boomerang Bro. fights alongside a Hammer Bro. and a Fire Bro. which the trio's name is "Hamma, Bamma, and Flare." The Hammer Bro. attacks by tossing his boomerang which can hit both Mario and his partner.

Super Paper Mario
Boomerang Bros are only encountered in The Overthere of this game. They can attack by throwing their boomerangs at Mario and the others. Oddly, even though they're part of the villainous Koopa Troop, they seem to have been sent to The Overthere. However, they most likely escaped to The Overthere along with the Skellobits when Bonetail broke away from The Underwhere.

Paper Mario: Sticker Star
Boomerang Bros are mainly found in World 3 in this game mostly in the first level Leaflitter Path. Boomerang Bros pose a much bigger threat as they can attack Mario twice in the same turn. Sometimes when defeated, Boomerang Bros drop Boomerang stickers which Mario can pick up and use them in battle himself.

Mario & Luigi: Dream Team
Boomerang Bros. are mainly seen in Somnom Woods. They attack mainly by throwing their Boomerangs at Mario and Luigi which the must dodge or hammer back. The Lakitus in the background help determine where the Hammer Bros. will strike.