SpongeBob keeps throwing the Mermarang to Barnacle Boy, and it returns to himself. On one occasion, he misses and the Mermarang is a "run-away." It injures most of the seniors, along with Mermaid Man and Barnacle Boy, which sends them to the hospital.
It is seen framed and put on display as part of SpongeBob's collection of Mermaid Man memorabilia.
It is a parody of a boomerang, and is also a parody of Batman's batarang due to being a boomerang weapon used by a superhero.