He is SpongeBob dressed as the classic Mermaid Man. He wears black and green pants with a orange belt that has a dark green "M". He also wears dark green gloves and a purple starfish on his nose.
He is SpongeBob dressed as the modern Mermaid Man. He has the same green gloves, black and green pants, and purple starfish on his nose. His belt is still orange but with a light blue "M" instead of green. He also wears a white wig and pink slippers.
Him and Barnacle Star are playing Mermaid Man and Barnacle Boy. He first answers the phone in his house and then runs outside to play Mermaid Man and Barnacle Boy with Barnacle Star. They then see Squidward, who they think is Doctor Negative, attack his vegetable garden, and eat his vegetables.
When Squidward is about to clobber Mermaid Pants and Barnacle Star, they remind Squidward that he is running late for work. Meanwhile, at the Krusty Krab, Mermaid Pants and Barnacle Star sing the Mermaid Man and Barnacle Boy theme song, annoying Squidward in the process. After he tries to get them to stop talking about Mermaid Man and Barnacle Boy, they see a fish with toilet paper attached to his foot, and they think he has been injured. Mermaid Pants and Barnacle Star mummify the fish, put him in a wheelchair, and add peroxide on his eyes, making the fish angry and moving away from them.
Squidward then tells them to take out the trash, but they punch the trash and make the Krusty Krab dirty, while the customers leave. After Mr. Krabs, dressed up as Captain Tightwad, and Squidward, dressed up as Dr. Negative, fight with Mermaid Pants and Barnacle Star, Mermaid Pants points out that no superhero should fight a supervillain unless said supervillain has committed a crime. They go to a bank for Captain Tightwad and Dr. Negative to pretend to rob it, until they get beat up by a security guard. Mermaid Pants decides to skip to the end of the story and picks up evil supplies for the villains.
Later, Captain Tightwad and Dr. Negative have Mermaid Pants and Barnacle Star over a pool of boiling oil, but Dr. Negative plots to actually fry Mermaid Pants and Barnacle Star. However, they tip over the lift and are set free, but Captain Tightwad and Dr. Negative get fried instead.
Mermaid Pants and Barnacle Star then fake drive into the distance.
"Man Ray Returns"
Shortly after entering Squidward's house to spy on their new temporary neighbor, SpongeBob and Patrick discover that the new neighbor is actually Man Ray. Upon finding this out, they go to the Shady Shoals Rest Home and discover that Mermaid Man and Barnacle Boy were put into "chronic sleep," also learning they would not be awake for another week. They then use Mermaid Man and Barnacle Boy's rings and turn themselves into Mermaid Pants and Barnacle Star.
Once they return to Squidward's house, where they first sneak in, they tumble downstairs soon after. They then cause a ruckus in the living room along with Man Ray, eventually being pulled up and causing him to snap and return to his evil self. Before they begin to battle however, the sound of thunder causes them to get frightened and fall down. Man Ray then receives a call from Squidward that he was returning early, and was expecting the house to be fully clean, which after he flees.
Mermaid Pants and Barnacle Star then use their saliva powers to fix up Squidward's house, albeit its later failure.