The Giant Fishballoon is a giant red puffer fish with a dinosaur-like tail and an oval body looking like an actual balloon. He has seven eyes and large fangs. He is also covered in giant spikes that go all down his back and tail. His lips resemble that of a balloon's mouth.
True to its name, the monster can expand his body and sucks air to inflate himself, which he possesses an incredibly powerful strength in fully-inflated state. He also briefly inflate bigger to cause his spikes to explode in all directions and destroying anything around him.
However, due to its balloon-like characteristics, he is very vulnerable to sharp objects despite his immense strength. The bowling alley star signs launched by the Girls instantly causes him to deflate and soars away crazily, propelled by the air rushing out of his body. He then falls on Mount Rushmore, squeaking out the last bit of air and completely weakened.
- In the episode "The City of Frownsville", The Giant Fish Balloon was seen crying. Later in the show, he was seen laughing when Lou Gubrious slipped on a banana peel. The Girls however, never fight him in the episode.
- Although he is not a main villain, he was treated like a main villain in the episode The Powerpuff Girls Rule! where he was featured along with the rest of the main villains, trying to get the key to the city.
- His physical appearance slightly changed in the episode "The City of Frownsville." In this appearance, he was shown to have yellow eyes instead of white, his fins were brown instead of orange, and his spikes were a dark shade of orange instead of the usual white.
- A "man in a rubber suit" version of him was featured in the music video for Signal in the Sky.
- In Demashita! Powerpuff Girls Z, he makes a short cameo appearance along with the original Powerpuff in the final episode.
- It is possible that he is an entire species as seen in Uh-Oh, Dynamo where a tiny Fish Balloon creature summoned the Giant Fish Balloon from the water to attack The Powerpuff Girls.
- Although it may be possible that these are the only two that exist.
- The sound effect when the Fish Balloon deflates was possibly recorded directly from deflating an actual balloon, rather than a pre-made artificial noise.
- The monster's design is based on Godzilla, Gamera, Titanosaurus, and Anguirus altogether; due to it's bipedal stance, it's tail, it's spikes, it's fins, and fire breath together. The tail's crystal spikes are based on the tail crystal spikes that SpaceGodzilla has.