25ft Under the Seat was uploaded to Newgrounds on September 27, 2008.
The episode begins with Tord getting ready to drive away; The gang each say their goodbyes - "Goodbye" (Edd), "Good Luck" (Matt), and "Good Riddance" (Tom). Tord then proceeds to hit Tom with his car and drives away. The group have a moment of reflection before Matt asks if they are going to start the next episode.
Tom is seen walking past the bathroom when he suddenly hears cries of distress from Matt, and backs away slowly. Matt then reveals to Edd, who is watching TV, that he accidentally flushed the key to the fridge down the toilet. Edd decides the group must flush themselves down the toilet to retrieve the keys. When Tom asks why they don't ask a plumber, he reveals the plumber's hand, still stuck in the drain of the sink. He then proceeds to flush Tom down the toilet before he can ask about a locksmith. The plumber then waves them goodbye, his hand still stuck in the sink.
When they emerge from the drains they find the city of Atlantis, where everybody is blue and has gills. They are called Atlanteans. After a short amount of time searching, they find that Matt's keys have become the new exhibit in a museum of wonders from above. The three end up going on a tour of the museum with the tour guide Simon. Eventually they find Matt's keys. But after taking it, Edd notices a security camera, which takes a picture of the trio stealing the keys from the exhibit. The Chief of Police then confronts the King with the picture of Edd, Matt and Tom stealing the keys. The king then orders the chief to summon the troops and spread posters over the town so they can capture the gang.
Later Edd, Tom and Matt find a wanted poster of themselves and decide they need to find a way out of Atlantis (Even though the pictures don't look like the trio). So they begin work on something that will help them escape. When they emerge they are seen wearing crudely made fish costumes but they manage to fool the police. A Cop called Frank almost rumbles them, until it is revealed his was pointing at a rock. The chief of police then tells Frank how much he hates him.
The trio then hide in the zoo, assuming they should be safe. It is, until Tom leans on a wall of glass marked 'Do not touch', the glass then shatters, releasing a giant purple octopus. The octopus angrily attacks Tom, making his life flash before his "eyes", then sends him flying. Edd and Matt try to run away from the creature, only to run straight into an angry cop and get captured.
In the next scene, the executioner announces their sentence to die by oxygen on charges of theft (retrieving Matt's keys) and releasing the octopus, and ties balloons around their necks. As sentence is carried out, they then start to float to the surface. While going up, Edd and Tom say goodbye, Edd apologizes for breaking Tom's bass (Ruined), and Tom apologizes for breaking his cat. When they reach the surface and realise they are not going to die, Tom says he wasn't really sorry about breaking Edd's cat, much to Edd's disappointment.
- Edd as himself, Simon and The King of Atlantis
- Tom as himself, Guard and Cops
- Matt as himself
- Bing as the Plumber and Kid
- Diwi as Frank
- PsyGuy as the executioner
This episode has received mixed reviews.
- When Tord gets into the car, he goes on the right side which is the British way of driving a car. But as he waves goodbye, he was on the left side, which is the American way of driving.
- Tord's car license says, "N0R5K1" or "NøRSKI", which is Norwegian for "Norwegian".
- The music that is playing when Edd and the gang are outside the city is a remix of the underwater theme from Super Mario Bros. (1985).
- One of the advertisements in Atlantis is for 'The world's largest free-range aquarium'.
- There is a road sign reading 'Road liable to flooding'.
- When they run into what seems like a zoo, the plumber's hand is seen inside one of the fish tanks.
- Matt's keys say "Kiss Me, I'm Ginger!"
- Outside the toilet is a picture of Tom and Edd standing beneath a street lamp which is a remake of an already existing photo.
- Matt breaks the fourth wall by asking Edd if they could start this episode.
- When Edd is watching TV, Diwi is on it. The other one on the TV may be Joe.
- On the welcome sign into Atlantis, it says "100% Water-Resistant".
- There is an Easter Island Head leaning against a building.
- A shop is called 'Don Eedit's Sushi Bar'.
- There is a fish person stuck in plastic beer nets with a sign saying "Please Help".
- There is a Tomee Bear in the leisure window of the museum.
- In the museum, there is a vine spelling out "Hello".
- The Tour Gide's next stop is "The Hall of Disregarded Underwear."
- In the wanted poster, Edd is depicted as having curved bangs, two different eyes, and with a nose, which the characters in Eddsworld aren't drawn with (outside of Canadians). Tom is seen with a more spiky Steve, a slightly more heart-shaped face, and wears sunglasses in place of his black-circle eyes. Finally, Matt is shown with a drastically extended square chin and flat hair, opposed to his swept up hair.
- When the Fish Policeman is pointing at the rock, there is a smiley face formed by the vines above the rock.
- On one of Tom's flashbacks, it reveals that Tom's mother is a bowling ball and his father is a watermelon, thus explaining why he was born with no eyes and a spherical head.
- However, it is later shown in Fun Dead that Tom's father is actually a pineapple which also explains Tom's spiky hair.
- In one of Tom's flashbacks, Matt appears to be sucking on a pacifier and is wearing his future purple hoodie instead of his original black hoodie and green jacket.
- In one of Tom's flashbacks, there's a Newgrounds poster on the wall.
- In one of Tom's flashbacks, Tom is wearing the same clothes of Stewie Griffin from Family Guy.
- In one of Tom's flashbacks, it is revealed the gang has met at the first grade.
- As the gang floated to the surface, Edd apologizes for breaking Tom's bass.
- As the gang floated to the surface, Tom apologizes for breaking Edd's cat, explaining the disappearance of Edd's cat Ringo, who appeared in Edd Again.
- Unintentionally, the executioner sends the gang back to the surface without harm, since he didn't realize that Matt, Tom and Edd live on the surface instead of under the sea.
- When the squid attacks, Tom shouts, "Life Flashing Before... hmmm." This alludes to him having no eyes
- One of the Atlanteans have the same design as the 3D main character on Edd's second channel, with big eyebrows and a purple shirt.
- There is a cola can with a lightbulb stuck to it in the museum.
- The plumber's hand makes a reappearance in Saloonatics.
- According to Matt, he suggested the idea of an Atlantis eddisode, but Edd said it sounded stupid. Two weeks later, he began working on 25ft Under the Seat and claimed he couldn't remember saying that.
- Most of this episode was written while Edd and Matt were on vacation in Devon.
- The title is a play on "2000 Leagues Under the Sea".