Of all the sea creatures in the world, alongside dolphins, octopuses, sea otters, and whales, the sneakiest sea creature alongside the shark 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 Seldom-Seen Species, probably because 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 its throat.
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.
- In One Piece there's Hammond, a villainous Small Name, Big Ego character who's also a Daggertooth Pike Conger fishman.
Film — Animated
- 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: 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.
- The Water Babies (1978): An electric eel serves as the sycophantic, brown-noser lackey of the evil shark king.
- 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".
Film — Live-Action
- 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.
- Large, carnivorous eels are a recurring danger in the Redwall 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 agrees to spare the heroes lives if they manage to release him from the pit. 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.
- 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.
- 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.
- Assassin's Creed IV: Black Flag: Spotted moray eels can be found hiding in seaweed, and they do attack Edward.
- 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., and return for Super Mario Odyssey now looking less cartoony and more like the demonic morays they were always meant to be.
- 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.
- Super Mario Galaxy features giant eels as enemies in water planets.
- Kaiju Combat: Moratitan the giant moray is not particularly friendly.
- 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.
- 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.
- 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.
- 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.
- DSBT InsaniT:
- White Killer Eels really live up to their name.
- Not only is Robber Eel, well, a robber, but he is slippery in the tricky sense too.
- 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").
- 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.