The Mermerang only made one appearance, in the episode "Shuffleboarding." It is a spoof of a boomerang.
The Mermerang is red and has scales on it, like the costume from Mermaid Man. It's a bit similar to a normal boomerang.
This weapon is one of Mermaid Man's weapons to defeat evil. SpongeBob keeps throwing it to Barnacle Boy, and it returns to SpongeBob. On one occasion, in "Shuffleboarding," he missed, and the Mermarang was a "run-away". It injured most of the seniors, along with Mermaid Man, and Barnacle Boy, and they in turn, had to go to the hospital.