Of all the sea creatures in the world, alongside dolphins, sea otters, and whales, the sneakiest sea creature alongside the shark and the octopus would be the moray eel. In nearly every form of media, eels are depicted as being sneaky creatures that have a propensity for tricking other sea creatures. It's a sure sign that they cannot be trusted. In other words, they're basically the oceanic version of snakes. Actual sea snakes (as opposed to mythical sea serpents) are less commonly used, probably because though highly venomous they're far less intimidating-looking than moray eels, which basically look very bizarre and downright alien, right down to having Xenomorph-like jaws in their throats.
Moray eels are the species most often used, due to their fearsome appearance, though the occasional Psycho Electric Eel may be used for this trope as well (despite electric "eels" being a type of knifefish). And sometimes, in an example of Artistic License – Biology, a moray will be a Psycho Electric Eel.
- Doraemon: Nobita's Great Battle of the Mermaid King have a giant moray eel monster larger than entire ships attacking the heroes when they arrived in the underwater world of Aquaria. Turns out it used to be a regular-sized moray, who was transformed into a monster thanks to the villains strapping a genetical manipulation device on it.
- In One Piece there's Hammond, a villainous Small Name, Big Ego character who's also a Daggertooth Pike Conger fishman.
- Prehistoric Park Reimagined: While largely portrayed as being more like aggressive animals than as outright villains, the two rescued species of Eocene eel rescued for the titular park nonetheless prove fairly dangerous animals to work with over the course of both the efforts at getting them through the time portal as well as subsequent efforts to move them out to a new holding tank so they won't be in the way for when the next rescued aquatic animal for that particular mission gets brought back through the portal (with one of them even managing to very nearly bite off one keeper's hand).
- The Little Mermaid: Flotsam and Jetsam are a prime example of this trope, two slippery moray eels working as spies for the villain Ursula. Unusually for Disney villain sidekicks, they are not humorous the least bit, averting Vile Villain, Laughable Lackey.
- Robin Hood (1973): When Prince John gets upset with Sir Hiss, he calls him an "eel in snake's clothing!" as he is a snake already, and therefore he had to go further than the typical insults.
- How the Grinch Stole Christmas!: According to the song "You're a Mean One, Mr. Grinch", the Grinch is actually "cuddly as a cactus and charming as an eel".
- Padak: Anago/Jooldom is an eel living in a sushi restaurant's aquarium with a bunch of other fish species. While everybody is pretty nihilistic about their situation, Jooldom stands out particularly for his Lack of Empathy, and is very creepy towards Naďve Newcomer Padak. Jooldom shows his true colors when he eats the corpse of Spotty, the nicest fish in the aquarium, an action which disgusts everybody else (which really says something as they previously had no compunctions about cannibalizing the other fish thrown in).
- The Water Babies: An electric eel serves as the sycophantic, brown-noser lackey of the evil shark king.
- Pirates of the Caribbean: Morey, from the Flying Dutchman's cursed crew, has an eel's head and neck as a personal mutation. Making the best out of it, it bites people in the face.
- A Sound of Thunder: One of the nastier bizarre Alternate History animals generated by the time waves is a gigantic eel. It uses ambush tactics for its initial attack on the hero, then bends its body like a hairpin to line up its jaws for another strike, while coiling its tail around him like a constrictor snake.
- Redwall: Large, carnivorous eels are a recurring danger in the books and serve as the series' equivalent to Sea Serpents and water dragons.
- In Mossflower, the heroes are captured by a tribe of hostile toads and thrown into a pit with a massive eel called Snakefish, whom the toads trapped there years earlier and used him to get rid of their prisoners since then. Surprisingly for a series in which fish are generally portrayed non-sentient creatures, Snakefish not only turns out to be quite intelligent, but fully capable of speech, and is able to be reasoned with. He agrees to spare the heroes’ lives if they manage to release him from the pit (he prefers the taste of toads to mice); but he does caution them that they must do so within a few days, before he must eat. They do, and Snakefish finally gets his revenge on the toads by devouring most of them.
- Taggerung features Yo Karr, another giant eel worshipped as a god by a tribe of pygmy shrews who sustain themselves on his offspring. In exchange, they regularly sacrifice some of their own to Yo Karr until Tagg kills him.
- In The Long Patrol, a yellow eel that is not quite as big as the two mentioned above, but still very dangerous to smaller animals, has settled in an abandoned well underneath Redwall Abbey and attacks a young nun before being killed by Skipper, the leader of the Mossflower otters.
- A Filk Song parody of Dean Martin's "That's Amore", titled "That's a Moray", centers around how dangerous eels are.
- Assassin's Creed IV: Black Flag: Spotted moray eels can be found hiding in seaweed, and they do attack Edward.
- Bug! has red coloured moray eels as enemies in Quaria. They stick out of wall areas to attack an unsuspecting Bug, and some of them can spit fireballs. While underwater.
- Carrie's Order Up! has Reginald, an eel businessman, complete with hat and suitcase. Of course, his slipperiness is limited to trying slip in as long a lunch break as possible.
- In Far Cry 3, moray eels are one of the three most dangerous creatures Jason Brody can come across in the waters of the Rook Islands, in addition to sharks and crocodiles.
- In Freddi Fish, Eddie the Eel is depicted as a trickster who prevents Freddi and Luther from trying to go where they needed to, unless he is bribed.
- GRIS: The black ooze that pursues the protagonist throughout the game takes the form of a gigantic eel that chases and snaps at her in the climax of the water level.
- Kaiju Combat: Moratitan the giant moray is not particularly friendly.
- A sub-section of the third Metal Slug game (first level, shortly after players take the submarine route) will have players encountering kaiju-sized morays who periodically lunged out from caves. They are invincible to missile or bullets, but they're not actively targeting the players - the morays are only interested in gobbling up equally huge jellyfishes in caverns on the other side of the screen, and the player character just happens to be in their way. At any rate the oversized eels serves more as random obstacles instead of enemies.
- Mega Man Zero: Volteel Biblio in Mega Man Zero 3 is a very sneaky character, his level being particularly trap-infested and snaking through secret passages all over his Boss Fight arena to get the drop on you, being That One Boss of the game.
- Pokémon: Huntail and Gorebyss are eel-like creatures that live in the sea; the former has characteristics of moray eels, viperfish and gulper eels, while the latter is based on the snipe eel and pipefish. Both are predator species, and use their respective characteristics to lure prey into range of attack.
- Shadow of the Tomb Raider: Moray eels team up with piranhas and plain old drowning to make your life miserable while underwater. Thankfully, and unlike piranhas, moray eels can be fought off and thus neutralized permanently without much trouble, so they look more intimidating than they actually are.
- Super Mario Bros.:
- Super Mario 64: Unagi the Eel is an infamous example. While not necessarily malicious, it does not appear to like Mario, as it will start roaring and swimming around if he comes close and contact with it causes damage. Unagi later becomes a type of enemy in New Super Mario Bros., appears as a track hazard in the Mario Kart Wii level "Koopa Cape" and the Mario Kart 8 level "Dolphin Shoals", and return for Super Mario Odyssey now looking less cartoony and more like the demonic morays they were always meant to be.
- Super Mario Galaxy features giant eels as enemies in water planets.
- Super Mario Sunshine: Eely-Mouth is a monster eel (that appears to be a hermaphrodite, oddly enough; some species are sequential hermaphrodites in real life) whose teeth are so bad that they somehow infect the water in Noki Bay, meaning Mario and FLUDD must go and clean things up, yet again.
- Donkey Kong Country: Tropical Freeze has a gigantic eel-like enemy called a Gargantuan Gill. A school of these things feature prominently in the aptly-named level "Twilight Terror", while a few more briefly appear later in the "High Tide Ride" level.
- DSBT InsaniT:
- Carmen Sandiego: In "The Crackle Goes Kiwi Caper", V.I.L.E.'s newest recruit for the position formerly held by Shadow-san is a particularly slippery sort, hence his code name "Neal the Eel".
- In Flipper and Lopaka, Serge is a sea snake (although easily mistaken for an eel) who acts as the 'brains' to Dexter's motivation. He is bright green, with a devious and sharp mind.
- In Hamster & Gretel, a Mad Scientist named Dr. Eelgood creates a giant mutant eel, calling it the "ideal eel." He plans to unleash it in the city aquarium as revenge from being fired from there. Hamster and Gretel stop his plan and defeat the eel by freezing it, but while Hamster is sending it away, he accidentally drops it and it shatters into a million pieces.
- SpongeBob SquarePants: In "Life of Crime", Mr. Krabs refers to a thief he saw on TV as an "eel in the kelp" (a play on the term "snake in the grass").