- SpongeBob SquarePants
- Patrick Star
- Mermaid Man
- Barnacle Boy
- Squidward Tentacles (cameo)
- Two mermaids
- Dirty Bubble
- Man Ray
- Realistic Fish Head (voice only)
- Human captain (debut)
- Human scientist (debut)
- Alien spaceship (debut)
- Gary the Snail (cameo)
- Moth (cameo as an action figure)
- Jumbo Shrimp (cameo as an action figure)
- Pi-Right Ponderer (cameo as an action figure)
- Bikini Bottomites
The episode begins at SpongeBob's house, where he and Patrick are preparing for a Mermaid Man and Barnacle Boy television marathon. As the first show, an "Origin Special" begins, SpongeBob's house loses power and then a wind rips the house and SpongeBob's TV away.
Mermaid Man then tells him a story, but it is not the actual story of his origin, it is actually the story of his washing machine being broken. Then, he tells another flashback, this time it is the origin story. In this flashback, Mermaid Man was washed off a beach and sucked into a raging whirlpool. Mermaids then rescue him and put a special starfish on his nose that allows him to breathe underwater. One day, Mermaid Man became lonely with his new life under the sea, when he saw a drowning Barnacle Boy and rescued him by using his powers to put barnacles in his lungs to give him the ability to breathe underwater as well. They then became partners, partly because Barnacle Boy was stuck breathing underwater for the rest of his life as a result of the rescue. They stopped a bank robber in the next flashback, then thwarted Man Ray in the next, but the two argue over the legitimacy of the flashbacks.
Then, the "actual" origin episode starts to air on the Mermalair's giant monitor, in which Mermaid Man (called Ernie in the story) and Barnacle Boy (called Tim in the story) are roommates. The following "origin episode" is full of nonsensical, random events. After cooking popcorn for movie night, they are thrust into an improbable series of events (with the even more improbable fact that it happened all at once), and eventually return to their apartment. The now-overcooked popcorn causes a radioactive effect on the two, giving them superpowers and the urge to fight crime underwater. They dive into the sea and start fighting crime.
As the show ends, Mermaid Man and Barnacle Boy are baffled by the ridiculousness of the episode. Finally, the camera cuts to SpongeBob and Patrick putting popcorn into a microwave with the intent to overcook it and give themselves powers.
The episode then ends with Mermaid Man and Barnacle Boy yelling "No! Stop!"
|( ‣ ) Associated production music|
|( • ) Original music|
|( ◦ ) SpongeBob music|
• Mermaid Man and Barnacle Boy Action Theme - Michael Bolger, Nicolas Carr, Pat Irwin [Title card]
‣ Arizona Fanfare - Jack Shaindlin [TV show]
• Mermaid Man and Barnacle Boy Action Theme - Michael Bolger, Nicolas Carr, Pat Irwin [SpongeBob and Patrick go over the checklist.]
‣ Arizona Fanfare - Jack Shaindlin [Mermaid Man watch]
‣ Crime & Danger Sign #3 - Hans Conzelmann, Delle Haensch [Start of marathon]
• Heroes to the Rescue - Nicolas Carr, Barry Anthony ["And now, without further fanfare..."]
‣ Excited Chase 1 - Phil Green [The pineapple blows away.]
• Watching Grown Men Prancing Around - Nicolas Carr, Marcin Pospieszalski [Squidward is watching ballet.]
‣ Excited Chase 1 - Phil Green [Squidward's house blows away.]
• Great Idea Patrick - Nicolas Carr ["Hey, that's it!"]
• Hot Steel and Slide Licks 5 - Jeremy Wakefield [Squidward blows away.]
‣ Against All Odds - Paul Lawler ["We have found the Mermalair!"]
‣ Fall to the Death - Harry Lubin [SpongeBob and Patrick fall into a net.]
• Lap Steel - Nicolas Carr ["Again!"]
• Befuddled - Pat Irwin [SpongeBob and Patrick laugh.]
• In the Beginning - Nicolas Carr, Marcin Pospieszalski ["In the beginning it was all dark."]
• Sponge Surf No Guit Me - Billy Lincoln [Young Mermaid Man surfs.]
• Aloha Lui Lui - Nicolas Carr, Sage Guyton, Jeremy Wakefield ["There I was in the ocean."]
‣ Dramatic Bridge 4 - Phil Green ["A wave drew me back into the ocean."]
‣ Dramatic Bridge 7 - Phil Green [Mermaid Man falling in the ocean]
‣ Rainbow Delights - Magnum Opus ["I was rescued by mermaids!"]
• Hot Steel and Slide Licks 2 - Jeremy Wakefield [Mermaid Man falls asleep.]
• Harps and Bells - Nicolas Carr ["There I was in the ocean."]
‣ Mount Olympus - Paddy Kingsland ["I had no other humans to talk to."]
• Sad Sack Shanty - Michael Bolger, Nicolas Carr [Mermaid Man sees a ship.]
‣ Masked Crusader 2 [#21] - Harry Bluestone, Emil Cadkin ["A boy in trouble!"]
‣ Pirate Ship - Harry Bluestone, Emil Cadkin ["Fear not, young man"]
• Hot Steel and Slide Licks 6 - Jeremy Wakefield ["No, no, no."]
‣ Arizona Fanfare - Jack Shaindlin ["Mermaid Man and Barnacle Boy!"]
‣ Mermaid Man and Barnacle Boy Action Theme - Michael Bolger, Nicolas Carr, Pat Irwin [A bank robbery occurs.]
‣ Heroes Salute - Harry Bluestone, Emil Cadkin ["Thank you, sir."]
• Mermaid Man and Barnacle Boy Action Theme - Michael Bolger, Nicolas Carr, Pat Irwin [Barnacle Boy defeats Man Ray.]
• Hot Steel and Slide Licks 7 - Jeremy Wakefield [Mermaid Man orders a pizza.]
‣ Arizona Fanfare - Jack Shaindlin [TV comes back on.]
‣ Sprightly Link 6 - Harry Bluestone, Emil Cadkin [Winchell Apartments exterior]
‣ The Bachelor Life (a) - Laurie Johnson ["Come on, Ernie, the movie's about to start."]
‣ Lost in the Galaxy [#35] - Harry Lubin [A scientist is doing tests.]
‣ Battle Zone - Harry Bluestone, Emil Cadkin [Ernie and Tim fall out of their apartment.]
‣ The Bachelor Life (a) - Laurie Johnson [Movie night]
‣ Imminent 4 - Harry Bluestone, Emil Cadkin [Reaction to overcooked popcorn]
• Mermaid Man and Barnacle Boy Action Theme - Michael Bolger, Nicolas Carr, Pat Irwin [Ernie and Tim become Mermaid Man, Barnacle Boy.]
• Hot Steel and Slide Licks 8 - Jeremy Wakefield ["Ah, feels just like yesterday, doesn't it?"]
• Slide Whistle Stooges - Nicolas Carr, Sage Guyton, Jeremy Wakefield [The ending]
- This episode is available on The Complete Eighth Season, Mermaid Man & Barnacle Boy: Defenders of the Deep, The SpongeBob SquarePants Collection, The SpongeBob SquarePants 8 Season DVD Collection, SpongeBob SquarePants Vol. 13, The Best 200 Episodes Ever, The Adventures of SpongeBob SquarePants, and Next 100 Episodes DVDs.
- In this episode, the mermaids' faces are drawn realistically.
- In this episode, Mermaid Man and Barnacle Boy's given names are revealed to be Ernie and Tim. These are nods to their respective voice actors, Ernest Borgnine and Tim Conway.
- However, in Mermaid Man and Barnacle Boy V, Mermaid Man calls Barnacle Boy "Kyle."
- Ernie is first bitten by a radioactively infected specimen of ant in "the apartment directly above," but when the two are flung back into their apartment, their window is shown to be on the top floor.
- Coincidentally, this and its sister episode "Plankton's Good Eye" both play "Slide Whistle Stooges" at the end.
- This is the first episode to mention telekinesis.
- This is the first episode in the SpongeBob SquarePants franchise in which the surface world is fully animated and not in live-action form.
- This was the last episode featuring Ernest Borgnine to air before his death on July 8, 2012. Two later episodes, "Super Evil Aquatic Villain Team Up is Go!" and "Patrick-Man!," were produced before his death and aired after.
- This is the final episode to feature Mermaid Man and Barnacle Boy. Due to the deaths of their respective voice actors, they have since been retired and now only appear on pictures or as toys.
- The episode's name is a direct reference to the 2005 movie, Batman Begins. This is further cemented by Mermaid Man and Barnacle Boy being direct parodies of Batman and Robin.
- The radioactive bug biting Ernie's forehead is a reference to Peter Parker (Spider-Man) getting bitten by a radioactive spider in the Spider-Man series.
- The bomb that explodes on Mermaid Man and Barnacle Boy is a reference to how Bruce Banner became the Hulk.
- The Big Splash is a parody of the Big Bang.
- The Vats of Acid "R" Us building is a reference to the stores Toys "R" Us and Babies "R" Us.
- Squidward's flooring gets smaller after his house is blown away.
- However, this is a common occurrence when seeing SpongeBob, Squidward, and Patrick's houses from the outside.
- When Squidward's power goes out, his TV goes out too, but his lights do not.
- When the solar eclipse is mentioned, it is really a lunar eclipse, not a solar eclipse.
- At the beginning of the episode, the first episode of the Mermaid Man Marathon is called the Origin Special, but at the end of the episode, it is called the Origin Episode.