The Atomic Flounder as a retired supervillain
The Atomic Flounder when he was younger, as seen in The Bad Guy Club for Villains.
The Atomic Flounder is a retired villain, from Mermaid Man and Barnacle Boy II, who can blast people, with his atomic breath. He fought Mermaid Man and Barnacle Boy. In The The Bad Guy Club for Villains, he resembles Harold.
Looks
In The Bad Guy Club for Villains, he has a shark fin, 2 fish hands and legs, a human hand, 2 alien eyes, and has a shark tail. In Mermaid Man and Barnacle Boy II, he is gray, has a green shirt with checkered pants and a black hat on his head.
Trivia
The Atomic Flounder's atomic ray, that was seen in Mermaid Man and Barnacle Boy II, is possibly a reference to Godzilla.
He was actually a fish in a lab experiment but it went haywire and he became the villain he is now.
His retired form looks like Flatts the Flounder.
The Atomic Flounder is the only retired villain and the only one who had aged.