"Mermaid and Barnacle Boy" is the 11 segment and half of the 6th episode of Season 1.
As SpongeBob and Patrick watch their favorite show, "Mermaid Man and Barnacle Boy," they dress up as then and think Squidward is a villain. After playing, and annoying Squidward at the same time, they visit them at a retirement home, and find out their retired, and try to get them out of retirement. After many failed attempts, they tick off the heroes, so they come out of retirement and uses nearby elderly fish and throw them out. SpongeBob and Patrick then watch "The New Adventures of Mermaid Man and Barnacle Boy."