The Mermerang has two different designs in the series. In "Mermaid Man and Barnacle Boy III," it was silver in color having a metallic appearance. In "Shuffleboarding," Mermerang is red and has scales on it, like the costume from Mermaid Man. It is quite similar to a normal boomerang.
The Mermerang was briefly seen in the episode "Mermaid Man and Barnacle Boy III" where it was seen on the wall of weapons along with the others. In "Shuffleboarding," SpongeBob keeps throwing it to Barnacle Boy, and it returns to SpongeBob. On one occasion, in "Shuffleboarding," he missed, and the Mermerang 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. In one episode SpongeBob gets his hands on the Mermerang and does not understand its function, and he accidentally injures Mermaid Man and Barnacle Boy.