- TV Narrator
- Mermaid Man (debut)
- Barnacle Boy (debut)
- Hammerhead Shark
- SpongeBob SquarePants
- Patrick Star
- Squidward Tentacles
- Reflecto (mentioned)
- Seas urchins
- Shady Shoals Caretaker (debut)
- Old Man Jenkins (wheelchair; blue; fat) (debut)
- Edna (debut)
- Gray Shark Resident (debut)
- Richard (debut)
- Old Sailor
- Orange Resident
- Mable the Gray Fish (debut)
- Cafeteria Workers (debut)
- Mable (debut)
- Dennis (debut)
- Man Ray (mentioned)
- Sylvester (debut)
- Lonnie (debut)
- Miss Shell (debut)
- The Chief (mentioned)
While pestering Squidward Tentacles, SpongeBob SquarePants and Patrick Star find out that their heroes, Mermaid Man and Barnacle Boy, are in fact living in the Shady Shoals underwater retirement home, and they then attempt to bring the two, (Mermaid Man and Barnacle Boy) out of retirement, much to the annoyance of the geriatric Bikini Bottom superheroes who only want their TV to get fixed. Star and SquarePants go through all kinds of hilarious antics, including painting the Boatmobile to faking a purse robbery, to reunite their superhero pals and eventually succeed, thereby creating Mermaid Man and Barnacle Boy's new show: The New Adventures of Mermaid Man and Barnacle Boy.
The phone gets broken, and when Mermaid Man hangs up the phone, a comic book bubble appears and dramatizes the words "HANG UP!" When Mermaid Man sits down, the bubble appears again and says "SIT!!" Will our heroes ever get their phone fixed? Tune in next week and find out. And when SpongeBob winks, the bubble appears again, saying "WINK!"
|( ‣ ) Associated production music|
|( • ) Original music|
|( ◦ ) SpongeBob music|
‣ The Lineman - Sam Spence [title card]
‣ Arizona Fanfare - Jack Shaindlin [opening]
‣ The Adventure Begins - Jonathan Neal [SpongeBob and Patrick dressed as Mermaid Man and Barnacle Boy]
‣ Enter the Villain - Chris Payne, Paul Rogers ["Reflecto, up to no good!"]
‣ Super Hero - Tony Hymas ["Donuts!"]
‣ Call to Destiny (a) - Ron Goodwin ["Creatures of the deep, assemble!"]
‣ Police Car - Sam Spence [a jellyfish appears]
‣ Death Trap - Gregor F. Narholz ["Reflecto has found our secret lab!"]
‣ Super Hero - Tony Hymas ["Mermaid Man and Barnacle Boy reunite!"]
‣ Hawaiian Link (b) - Richard Myhill [rest home exterior]
‣ Seaweed - Steve Belfer [Mermaid Man, Barnacle Boy watching TV]
‣ War Agitato - Jack Shaindlin [Mermaid Man panics]
‣ Hymn of Achievement [#7.03] - Gregor F. Narholz [SpongeBob's speech about old people]
‣ Queen's Aloha Oe (b) - Kapono Beamer, Queen Lili'uokalani [lunch]
‣ You're Nice - Sage Guyton, Jeremy Wakefield ["Do you remember when the food supply in Atlantis was running low?"]
‣ Wedding Procession - Felix Mendelssohn-Bartholdy, Leslie Pearson [SpongeBob kicked out]
‣ Hawaiian Link (a) - Richard Myhill [later...]
‣ Sweet Annabelle - Sam Fonteyn [SpongeBob dressed as a lady]
‣ Blackbeard - Sam Fonteyn [Patrick dressed as a burglar]
‣ Blood in the Gutter - Laurie Johnson [Mermaid Man sleeping with eyes open]
‣ SpongeBob Closing Theme - Steve Belfer, Nicolas Carr [painting the Invisible Boatmobile]
‣ War Agitato - Jack Shaindlin ["Evil!"]
‣ Arizona Fanfare - Jack Shaindlin [fanfare]
‣ The Lineman - Sam Spence [water balls]
‣ Moloka'i Nui (a) - Kapono Beamer ["I feel five years younger."]
‣ Arizona Fanfare - Jack Shaindlin [SpongeBob and Patrick watching the new show]
‣ Caped Crusader - David Farnon [Mermaid Man and Barnacle Boy playing checkers]
‣ Police Car - Sam Spence [sting at end]
- This episode is available on the Tales from the Deep, 10 Happiest Moments, Absorbing Favorites, The Adventures of SpongeBob SquarePants, Complete 1st Season, and First 100 Episodes DVDs.
- As of May 14, 2017, The Internet Movie Database (IMDB) gives this episode a rating of 8.6/10 based on 420 ratings by users. TV.com users give this episode a 8.7/10 based on 217 votes.
- "Mermaid Man and Barnacle Boy" was ranked #37 during the Best Day Ever event on November 9–10, 2006.
- This episode marks the first appearance of Mermaid Man and Barnacle Boy.
- Mermaid Man and Barnacle Boy have five fingers as youngsters, though as elders, they have four. This could be a technical fault since four fingered gloves were easier to draw.
- When SpongeBob and Patrick are first asking the man at the front desk to see Mermaid Man and Barnacle Boy, an article on the inside of his newspaper reads, "School Drop Out Rate Soars." This has double meaning because "school" is also the name of a group of fish.
- The old captain is played by the man who guards the gates at Nickelodeon Animation Studio in Burbank, California. He is also the inspiration for the character "Old Kid" from Invader Zim.
- When Mermaid Man picks up the phone during the game of checkers, the phone's ringtone is the same sound effect used for number 11 of the thirteen bad words in "Sailor Mouth."
- Running Gags: Mermaid Man screaming "EVILLL!," SpongeBob and Barnacle Boy saying "There's evil afoot!," and the winking old man.
- This is the only episode in which the Mermalair is called the Sea Cave.
- This is the first of the Mermaid Man and Barnacle Boy series.
- This is the first episode to use music from the NFL, "The Lineman," which was used in most of the Mermaid Man and Barnacle Boy episodes.
- Before SpongeBob and Patrick are watching TV, when Mermaid Man talks with Barnacle Boy, there were two Old Man Jenkins, Green and Blue.
- This is the fourth episode to use live action sequences.
- This marks the first appearances of Mermaid Man, Old Men Jenkins, Dennis, Mary, Mrs. Shell, Lonnie, Sylvester, Richard, Mable, Other Residents and Shady Shoals Rest Home.
- This episode contains the first mention of Man Ray, although, Man Ray wasn't seen until "Mermaid Man and Barnacle Boy III."
- During a tribute to Ernest Borgnine, this episode was paired with "Mermaid Man and Barnacle Boy II."
- The sequels to this episode used the same title card art until "Mermaid Man & Barnacle Boy VI: The Motion Picture."
- This episode premiered on Stephen Hillenburg's 38th birthday.
- Atlantis is first mentioned in this episode before making its first actual appearance in the episode "Neptune's Spatula."
- In the episode "Jellyfish Jam," Squidward said that SpongeBob is the only guy he knows who can have fun with a jellyfish, but in this episode he relaxes with a jellyfish. This may mean that this episode takes place after "Jellyfish Jam."
- The ironic thing about this is that in most comic books, the dramatization of simple words usually comes in on action fighting scenes, but in this SpongeBob episode, it exaggerates the word dramatization as a reference to the 1960's Batman TV series.
- Mermaid Man and Barnacle Boy are parodies of both Aquaman and Aqualad and Batman and Robin.
- The Adventures of Mermaid Man and Barnacle Boy is a parody of the Batman TV show from the 1960's as well as that of Filmation's Aquaman animated series.
- The Aqua Phone is a parody of the Bat Phone from Batman. It is also a possible parody of the Hotline Phone from the Powerpuff Girls.
- The Invisible Boatmobile is a parody of both Wonder Woman's Invisible Jet and the Batmobile.
- Reflecto may be a parody of Electro.
- The Sea Cave may be a reference to the Batcave.
- When SpongeBob and Patrick are performing the "Burglar" attempt, the way SpongeBob says help, (Hay-ulp!) is a direct reference to The Perils of Penelope Pitstop, in which the main character Penelope Pitstop's catchphrase is that exact line.
- When Patrick takes the doughnut from the box, it is orange, but when they "unite," it is replaced with the chocolate one which was left in the box. After that scene, it changes to the normal doughnut again.
- After Patrick takes SpongeBob's purse and peers out from behind the building, the purse is seen floating beside him.
- Barnacle Boy puts the wrong ring on Mermaid Man's hand.
- After Mermaid Man says the oath, both his and Barnacle Boy's rings disappear.
- Mermaid Man illegally moves one of his checkers into a red space before the screen switches to "King Me!"
- Many illegal moves had to have been present before the show begins as you can see multiple pieces on red squares. Either the undersea version of Checkers has vastly different rules, Mermaid Man and Barnacle Boy are too senile to remember how to play, or this is an error.
- Also, on Mermaid Man's last move, he moves 3 spaces forward and 1 to his left. This results in an impossible jump (which captures no pieces) or an illegal move.
- When Mermaid Man and Barnacle Boy say "Dog paddle, away!" and start dog paddling, you can clearly see Mermaid Man's socks are missing. Afterwards, they return.
- When Mermaid Man says "Up, up and away" while rocking, Barnacle Boy appears to be saying it too, but with no voice.
- Also, the animation appears wrong.
- In this episode, Mermaid Man and Barnacle Boy are revealed to have come out of retirement but in later episodes they seem to be still staying in Shady Shoals, such as in "Night Light," "Mermaid Man & Barnacle Boy VI: The Motion Picture" and "Shuffleboarding."
- When Mermaid Man says "To the broccoli!" His right bra strap turns orange for a split second.
- After Mermaid Man and Barnacle Boy say "Dog Paddle away!" Mermaid Man is not wearing tights.
- When Mable comes outside after Mermaid Man says, "sea creatures assemble," the bottom of her cane flashes white for 2 different frames.
- In the GBA video SpongeBob SquarePants Volume 2 episode menu, the episode is mistakenly named "Mermaidman."