Plankton decides to destroy the Chum Bucket and turn it into a coliseum, announcing to Bikini Bottom on a jumbotron there will be free entertainment, promising guts and glory available to everyone in now what is called the Chum Coliseum. The coliseum is a spoof of the Roman coliseum with its battles and gladiatorial games, complete with Plankton in the Emperor's chair and a toga. Soon, the Krusty Krab is devoid of its loyal customers and Mr. Krabs and the crew go to the coliseum to find out what Plankton is up to. When they sit down, a giant Lion Fish is released and SpongeBob is excited until he realizes the prisoner that will be going up against the Lion Fish is Patrick. To entice the Lion Fish into chasing Patrick, Plankton orders blood sausages to be placed around Patrick's throat. SpongeBob decides to help Patrick and turns into a gladiator, complete with armor and a chariot pulled by sea horses.
He soon catches up with Patrick and rescues him, but now the entertainment has turned into a chase scene that doesn't contain the blood and guts Plankton promised even Betsy Krabs wants to see "body parts." Meanwhile, Plankton is trying to sell chum to the crowd who are getting hungry waiting for the guts and glory. One of the spectators agrees to buy a chum stick, but is angered when Plankton tells her it will be $10. She asks why she should pay $10 when Krabby Patties are only a single buck, which Mr. Krabs agrees to. Plankton angrily tells her "You can't get entertainment like this at the Krusty Krab!" and states that the fight will be off unless she pays $10. She agrees and immediately gets sick from eating the chum stick, while the rest of the crowd, having had enough, gets up to go. Plankton traps all the customers by blocking all the exits when they try to leave. He claims to have waited 20 years to see the amount of customers Mr. Krabs sees every day and demands everyone to sit back down and buy his chum. They sit back down grumbling and the entertainment continues.
Going back to SpongeBob and Patrick, SpongeBob discovers that the Lion Fish is chasing the blood sausages around Patrick's neck, not them, after witnessing the Lion Fish eat a sausage that was thrown on the ground. He throws the rest of the blood sausages and they land in a pile on Plankton. He freaks out, now realizing the Lion Fish is charging towards him. He quickly escapes out of a secret door he placed in the coliseum, taunting the Sea Lion and calling it a "prissy feline." The Lion Fish smashes through the wall and chases Plankton who runs for his life. After Plankton's failed plans, the Krusty Krab is back in business, but Mr. Krabs has raised the price of a Krabby Patty from $1 to $10. When a customer complains about it, Mr. Krabs points to the Lion Fish and tells him he can take it up with his new "financial advisor." Mr. Krabs, SpongeBob, Patrick, and Squidward laugh together then leave rather awkwardly one by one. The episode ends with the Lion Fish roaring.
Chumsticks come in two shapes: Square and corndog shaped.
According to this episode, the secret formula for Plankton's chum is: whale blubber, jellyfish squeezings, seahorse snout, and just a sprinkle of anchor rust. That means Plankton's chum is different from common chum.
In the much later episode "Jailbreak!," Plankton used an alternate way of creating chum.
There could be several different methods to make chum.
He could have also been lying to not tell people that it's made of fish.
Angry Jack can be seen in the audience of the coliseum.
When SpongeBob gets in the chariot, his clothes transform into Roman gladiator armor.
Like the Sea Bear from "The Camping Episode," the Lion Fish is portrayed as a fish with a predatory animal's head, and claws on the tips of its pectoral fins.
In this episode, Plankton says he has waited for 20 years to get the amount of customers Mr. Krabs sees everyday. However, in "Plankton's Army," it was the 25th anniversary of Plankton stealing the Krabby Patty Formula. This suggest that this episode takes place five years before that episode.
The title card is a parody/reference to Ancient Greek text, but the "U" in Spongicus is not shaped like a "V" like it would have been back then. However, this could have been done to make sure the audience could read the title card.
The title "Spongicus" is a spoof of the infamous Roman gladiator Spartacus.
The coliseum that Plankton made is similar to the Colosseum of Rome.
The Lion Fish is a parody of the Neamean Lion from Greek mythology and a visual pun on real-life "Lionfish."
When the people were leaving the Colosseum, they wound up in the area of the arena. Plankton (while riding on top of Karen) was also in the arena when vending chumsticks. In reality, they could not go from the bleachers to the arena; corridors would lead from the bleachers to the outside of the Colosseum.
Also, the chariot and the Lion Fish weren't there. Maybe they just took a break from performing.
In the beginning of the episode, SpongeBob warns Mr. Krabs about Plankton through a payphone. However, the payphone disappears in later scenes and is not seen for the rest of the episode.
Patrick's toga is white, but in one scene, it was green.
Plankton tried to boil Mr. Krabs in a giant bisque. This doesn't make sense as "bisque" may refer to unglazed white pottery or a type of seafood soup, not a container. But it's possible:
Plankton actually used a bisque pot to boil Mr. Krabs, but bisque wouldn't be able to hold molten liquid, which is possibly the reason Plankton failed.
Plankton wanted to boil Mr. Krabs with molten liquid, then put him in bisque soup.
Patrick's lips turned pink, instead of black, towards the end of the episode.
SpongeBob uses a payphone that just appeared there.
Somehow, Plankton changed his clothes and got inside from his wrecking ball in a matter of seconds.
Plankton accepts $10 from a customer, and then it disappears.