Barnacle Boy is tall, thin, bald, has a very large nose (similar to and bigger than Squidward's), has puffy ears, a sailor hat, a black mask and a turquoise neckerchief. He also wears dark blue rubber gloves, boots, a red T-shirt, and rubber black shorts. Being younger, he is more sane and self-aware than Mermaid Man. However, Barnacle Boy is also more cranky and rude. He often calls Mermaid Man an "old coot." He is revealed to be 68 years old in "Mermaid Man and Barnacle Boy V." As his younger self, instead of a black mask, he wears glasses and is much taller. Also, as younger self, his neckerchief is space-control.
Barnacle Boy possesses powers similar to Mermaid Man, though he lacks the belt powers. Barnacle Boy also has "Sulfur Vision" (a form of Heat Vision), which Mermaid Man has never been shown to have. Like Mermaid Man, his powers do not work as well as they used to, mostly due to old age.
Despite being a senior citizen, Barnacle Boy is still treated like a child by his mentor, much to his disdain. In "Mermaid Man and Barnacle Boy V," when Mermaid Man orders a Pipsqueak Patty (a very small version of a Krabby Patty, intended for children) for Barnacle Boy at the Krusty Krab, they get into an argument which ultimately results in Barnacle Boy becoming a villain and forming a group called "E.V.I.L." (Every Villain Is Lemons) with Man Ray and the Dirty Bubble. After a protracted fight with Mermaid Man and the "International Justice League of Super Acquaintances (whose costumes and powers are assumed by the main characters of the show), which E.V.I.L. actually wins, he and Mermaid Man patch things up. Barnacle Man, as he likes to be called, gets a little more respect now (even though he mentions that an adult-sized Krabby Patty actually is too big for him).
Mermaid Man & Barnacle Boy are in Rock Bottom when Patrick and Mermaid Man have a soda drinking contest. Patrick wins but Mermaid Man gets injured and SpongeBob finds help to get him in the Invisible Boatmobile. Mermaid Man & Barnacle Boy later leave Rock Bottom. At the end of the game, they are at Neptune's Paradise with SpongeBob.
Mermaid Man & Barnacle Boy appeared during a new episode being directed by Gill Hammerstein. In the new episode, Mermaid Man & Barnacle Boy were falsely accused for destroying the Sand Stadium when it was actually stolen by the Sneaky Hermit. However, when they were sent to Bikini Bottom Jail, the prison warden told them what's really going on and lets them go so they can catch the villain, thus accidentally letting the Dirty Bubble and Man Ray go free. Mermaid Man & Barnacle Boy went to Goo Lagoon and to the Krusty Krab to find clues. When they went to the Chum Bucket, they discovered that Man Ray and the Dirty Bubble are using the mayor's child as their captive in an attempt to help the Sneaky Hermit's plans. They reluctantly made a truce with the villains and worked together to find the Sneaky Hermit with some help from an expert hunter from Jellyfish Fields. They managed to track down the hermit and foiled his plan of putting Bikini Bottom on his back so he can have a home. When the crisis ended, they returned to the Sand Stadium to continue watching the musical performance, to which Mermaid Man thinks it's a football game.
Mermaid Man and Barnacle Boy appear when SpongeBob and Patrick want to borrow the invisible Boatmobile. They later appear when SpongeBob gets his "license" from Seymour. Mermaid Man & Barnacle Boy later arrest Seymour and Mermaid Man calls him evil. They are also unlockable characters who drive in the same boat during the races.
He has hair growing out the wrinkles on his liver spots.
Barnacle Boy had become a superhero during the 1960s-like era.
Barnacle Boy has a case of cauliflower ear, in which the ear becomes swollen and deformed. This condition is commonly seen in elderly people.
There was a Dorf episode where he plays bingo, and in "Mermaid Man & Barnacle Boy VI: The Motion Picture," the two heroes are playing bingo (though Mermaid Man gets it wrong by shouting "Bonko!" instead of "Bingo!," much to Barnacle Boy's annoyance).
In the Russian dub, Barnacle Boy had his name changed several times. Initially, in the first three Mermaid Man and Barnacle Boy-centered episodes, his name was "Очкарик," which roughly translates to "Glasses Boy," then in "Mermaid Man and Barnacle Boy IV," his name was "Прилипала," which roughly translates to "Suction Boy." In "Mermaid Man and Barnacle Boy V," his name was "Юнга," which roughly translates to "Sea Cadet," and in "Mermaid Man & Barnacle Boy VI: The Motion Picture," his name was "Малыш-Ковбой," which roughly translates to "Cowboy Kid."
In the German dub, Barnacle Boy is called "Blaubarschbube," which translates to "bluefish boy." This is not the only instance in SpongeBob where "barnacle" is translated as "Blaubarsch," the other being The Ugly Barnacle (ger. Der hässliche Blaubarsch).
Barnacle Boy's real name is Tim, which is a nod to the first name of his voice actor, Tim Conway.
Mermaid Man's real name, Ernie, shares the same attribute too, to his own voice actor, Ernest Borgnine.
"I'm tired of playing second banana to a man who wears a bra!" (to everyone in the Krusty Krab)
"I'm 68 years old and I want a Krabby Patty!" (to Mermaid Man)
"Listen Big Nose, that guy has been saving your butt since before you were born. Don't you got a 'Living Legend Discount' or something?" (to Squidward)
"You don't even remember breakfast, you old coot." (to Mermaid Man)