The Atlantisians are the citizens of the underwater city Atlantis. They are blue-skinned humanoids with gills on their neck, black eyes and no hair. They are the main antagonists of Eddsworld episode "25ft Under the Seat".
When Matt accidentally flushes the key to the fridge down the toilet, Edd, Tom and Matt decide to flush themselves down the toilet to get their keys back. They ended up in the underwater city Atlantis where blue humanoids live. The gang goes on a tour of the Museum of wonders from above with the tour guide Simon. They find out Matt's keys have become the new exhibit. Matt grabs them, but the security camera takes the picture of them. The Chief of Police shows the picture to the King who orders him to summon the troops and spread posters over the town.
Later, the gang notices a wanted poster of them. To escape from the cops and city, they masked themselves as fish, fooling the police. A cop called Frank only notices them, but it is then revelaed he is pointing at a rock with some mollusks on it. Angry Chief then tells him he hates him so much.
The gang hides in the zoo, but Tom mistakenly breaks a wall of glass marked 'Do not touch' and releases the giant purple octopus out. The octopus attacks Tom angrily. Meanwhile, Edd and Matt try to run away, only to bump into the cops. For taking the key and releasing the octopus, the gang is sentenced to death by oxygen. The Executioner ties balloons around their necks and they start to float to the surface. Luckily, when they reach the surface, they realize they are not going to die, as oxygen isn't deadly for them.
- The scene where the King's head turns into a realistic fish head, is a reference to SpongeBob's character Johnny Erain.
- 'Death by oxygen' should probably be 'Death by air' as fish breathe oxygen as well. However, Atlantisians could breathe another element or chemical.
- The Executioner obviously thought Edd, Tom and Matt are aquatics creatures just like him, because he didn't realize they can breathe on the surface.