SpongeBob is waxing Gary when the local mailfish shows up and hands SpongeBob a videotape. SpongeBob plays the tape on his TV, which says that he has been crowned "King of Karate" and tells him to go to "Karate Island" to be crowned.
SpongeBob is about to leave when he encounters Sandy, to whom he happily explains that he is the King of Karate. Sandy is suspicious of this, so she accompanies SpongeBob on the boat ride. The boat stops at Karate Island, where the guru, Master Udon, greets SpongeBob, but ignores Sandy. SpongeBob, to prove his Karate skills, asks to fight Master Udon's best guards. Three guards arrive, and when they fight SpongeBob, they pretend to get hurt and soon pretended to be defeated.
Sandy notices this, adding to her suspicion. SpongeBob is officially crowned "King of Karate" and sits on his throne and requests Sandy to sit beside him in a lounge chair. Sandy leaves when SpongeBob becomes arrogantly proud and accuses her of being jealous of him. After she leaves, SpongeBob is suddenly locked into his throne. Just as the water is up to Sandy's head (she was walking into the water), she hears SpongeBob's cries for help, and reluctantly goes back to save him.
Sandy fights through Udon's castle, fighting an opponent on each floor with an unusual "power" (there are three floors that Sandy has to get through) until she crashes through the top floor's entry way; the trapdoor where SpongeBob is being held hostage by Master Udon. Udon reveals that he is a real estate agent, and won't let SpongeBob go until he agrees to buy a time-share condo on the island, while also increasing his equity. He then tells SpongeBob he is not king of karate, but could be king of condos. SpongeBob shouts in horror and Sandy attempts to fight Udon, but he drops a sturdy bamboo cage on her, which she quickly breaks out of with meditation, strange hand movements and weird muttering. Master Udon rips off his robes while Sandy rips off her jumpsuit to expose her bikini and after a brief muscle growth in their swimsuits the two begin fighting, (Udon's extra muscles were in his eyebrows, and Sandy's were in her tail) and Sandy defeats Udon by kicking him out of the room into the water below. She frees SpongeBob, and the two leave the island.
The episode ends with Squidward arriving on "Clarinet Island" to be crowned "King of Clarinets," and him being looked down upon by Master Udon.
The original airing had a small amount of blood on Master Udon's face after being beat up by Sandy. This was removed due to being deemed too violent for a TV-Y7 show. The dedication card at the end of the episode was removed after the Best Day Ever Marathon.
The episode originally ended with a dedication to Noriyuki Pat Morita (1932–2005), also known as Mr. Miyagi from The Karate Kid series, who voiced Master Udon in this episode and died on November 24, 2005. The online version, the Polish airings, the Canadian airings, the Spanish airings, the German airings, the Philippine airings and DVD versions still have the dedication.
This episode is dedicated to Pat Morita (voice of Master Udon) who died on November 24, 2005 due to kidney failure.
In the UK, this episode carried a PG classification from the BBFC due to the comic violence.
The painting of a boat inside Gary's shell is a replica of the painting over The Simpson's family couch.
Udon is named after a Japanese/Korean noodle soup. When Sandy defeats Udon, she says: "You're in the soup now, Udon!"
This episode is noted to be one of the most violent in the series, due to the scene when Sandy breaks Master Udon's leg, during the karate fight.
In Germany, this episode is called "Der König des Karate" (The King of Karate).
In the Greek version of this episode Squidward (at the end) says Είμαι εδώ, είμαι ο βασιλιάς του Καράτε και είμαι εδώ which means I am here, i m the king of Karate and i m here but he should say Clarinet instead of Karate..
When Sandy throws jelly filled donuts at The Tickler, the first shot of the plate shows that there are barely any left, but the second shot shows the plate full of donuts again.
The Tickler's mouth full of jelly filled donuts that Sandy used to attack is similar to Patrick's mouth full of snowballs that SpongeBob used in "Snowball Effect."
In the scene where Sandy fights the enemies on each floor, the dialogue is dubbed, similar to old style Kung-Fu films.
Sandy's helmet protects Sandy from Filthy Phil's body odor, but in other episodes, Sandy's helmet doesn't protect Sandy from any smell at all such as Squidward's belch stench from "Squidtastic Voyage."
This is the first episode to have sound effects on title cards.
The first few airings of the episode said: Pat Morita (1932–2005) with a picture of him. Later, Nickelodeon took this off.
None of the four stages of doom use Karate except when Sandy fights Master Udon.
Udon said there Four Floors of Fear, but Sandy only went through three. Udon's floor possibly counts as one.
It was unknown how or why Squidward was made king of clarinets, but it is possible he got the same video, and then found out it was a condo similar to SpongeBob.
Filthy Phil can smell his own body odor, but in the episode "Something Smells," SpongeBob didn't smell his own bad breath.
There may be some references to Naruto. As when breaking out of the Cage, Sandy does hand seals and she breaks out.
When Lip Service says: "Dance, Squirrel, dance," it is a possible parody of The Rocky and Bullwinkle cartoons where Natasha Fatale says: "squirrel" in the same accent. It might also be a reference to an old Looney Tunes episode where Yosemite Sam says to Bugs Bunny "Dance, Rabbit, dance."
The scene in which Master Udon falls through the wall and lands in the water is a redo of the last scene of Game of Death, where through an aerial view, the villain is seen falling down to the streets, after being kicked off a balcony by Bruce Lee.
This episode contains many references to films Game of Death and Kill Bill: Sandy's yellow jumpsuit is a reference to the jumpsuit that both Bruce Lee and Uma Thurman wore in their respective films. Also, the concept of fighting an opponent on each floor is also present in both of these films.
This episode is also similar to a series of episodes in the Red Ribbon Army saga of Dragonball, where Goku tackles six floors of challenges. This episode is also attributed as a reference to Game of Death.
Sandy's and Udon's muscle growth is loosely based on Toguro's 100% muscle growth in the anime Yu Yu Hakusho.
When Sandy kicks Master Udon in the face, she has five toes, but she usually only has three.
When Master Udon throws Sandy in the wall, her helmet doesn't break although it should.
It is unknown how SpongeBob got out of the chair that he was cuffed to.
When The Tickler says "Oh no! Jelly-filled donuts? How did you know they were my weakness?" his voice is out of sync with the animation. However, this may have been done intentionally as a parody of English animie dubs.