The Tsuchinoko (translated to English as "child of hammer" or "child of dirt") is the name of a small, snake-like creature in Japanese legend, known for having a disproportionately pudgy body ending in a slender, pointed tail. They are typically jet-black or dusty-brown and can be as long as 12 to 31 inches. Their behavior is noted to be strange, defying behavior seen in similar animals and even defying certain laws of physics. They can bite the end of their tail to form a wheel to travel faster to avoid predators or catch prey and they can even Double Jump by scrunching their bodies like an accordion and unloading like a spring. The tsuchinoko is a viper and thus has fangs filled with venom, but unlike other snakes, they don't hiss, but squeak and chirp instead. They are most commonly seen in Western Japan, mostly in Kansai and Shikoku.
The Tsuchinoko is classified as equal parts Youkai, mythological creatures used to explain natural phenomena like fairies and spirits, and cryptid, creatures with evidence that they may theoretically exist like Bigfoot and the Loch Ness Monster. Much like Bigfoot in America, Tsuchinoko has had a bounty for its capture by the local government of Yoshiicho Yoshi in yen to the equivalent to $1,000,000 US, with various other sightings and bounties made as far back as 712 A.D.
- In Kemono Friends, one of the Friends is a tsuchinoko. Appropriately, she's shy and likes to hang out in secluded areas.
- Occult Academy: Several shorts exclusive to the DVDs center around a pet tsuchinoko kept by Maya and Ami.
- QT in Space Dandy catches a few during his brief interest in fishing. They seem quite easy to come by though one of the tsuchinoko's is actually a shapeshifting Chameleonian.
- In 3×3 Eyes, at one point Benares is seen resting on a roof, leaning against a massive snake-like cyclopic creature which greatly resembles the traditional depiction of a Tsuchinoko (a massive, fat-bodied snake with a very small tail).
- In Star★Twinkle Pretty Cure, Lala dresses up as one for Halloween in episode 37.
- Folklore in United States, Canada, Australia and Greece all have different variations of a mythological creature called the Hoop Snake (or in Greece's case, the ouroborous), a snake that could allegedly bite the end of its tail to form a wheel similar to the tsuchinoko. The US version in particular has appeared in many famous folktales, including several of Pecos Bill's exploits.
- Yu-Gi-Oh!: There are three Tsuchinoko cards; Danger!? Tsuchinoko?, Sinister Serpent and Terene Tootheed Tsuchinoko. All three monsters are weak, but have interesting effects.
- Castlevania: Aria of Sorrow: There's a tsuchinoko as a particularly elusive enemy that serves as a Metal Slime not because it drops a lot of money if killed, but because possessing its soul reduces prices at the shop. It appears in a single room, and not every time you enter it, and tends to disappear quickly. Once you do so, the bestiary description states that Soma claimed the bounty for proving its existence.
- Vitium's baby form in Digimon World Re:Digitize was designed to resemble the Tsuchinoko, being a small, pudgy, rather cute snake-like creature.
- Final Fantasy XIV's Shadowbringers expansion has the Great Serpent of Ronka that's one of these, being a chubby worm believed to be the avatar of the gods that guided the ancient Ronkans in the past. The player earns one of these as a non-combat pet after a series of quests.
- Metal Gear:
- Metal Gear Solid 3: Snake Eater: You can catch a tsuchinoko if you're lucky. Which is odd, since the game takes place in Russia. The team congratulates you when you do and you get an achievement (in the HD remake). You can even eat it, which would be a stupid thing to do since finishing the game with a live tsuchinoko in your inventory rewards you with a facepaint option that grants Infinite Ammo (and don't worry; if you already caught it, the critter can be easily recaptured following a plot-relevant event that dumps all of Snake's inventory).
- Metal Gear Solid: Portable Ops: "TSUCHINOKO" is a possible end-of-campaign codename the player can earn. It's the third-worst codename in the game (after "PIGEON" and "KEROTAN", generally reserved for the worst possible playthroughs) and basically involves engaging with the game as little as possible; no alerts, no deaths, recruited soldiers and saved infreqently. In short, it's a codename for players that are about as elusive as its namesake.
- Metal Gear Solid V: The Phantom Pain: The tsuchinoko is just one of many animals Venom Snake can capture for Diamond Dogs's makeshift animal reservation. Appropriately, it's one of the rarest animals in the game, only found in a tiny dead-end area in the Angola-Zaire border region, and even then Snake doesn't actually get to lay eyes on it in the field; it has to be captured with a mouse trap like in MGS3.
- Metal Gear Online: The MGS4 and MGSV iterations "award" the Tsuchinoko codename and emblem for players that don't log in for a lengthy period of time (typically a month), once again comparing the player's elusiveness to the namesake cryptid.
- Monster Hunter: World: It's possible to capture a tsuchinoko and keep it as a pet. However, they're incredibly rare since they're only available for capture during the Kulve Taroth event.
- Pokémon: Dunsparce is a tsuchinoko with small wings and a rattlesnake-like tail (that's actually a drill). They are very elusive, and spend most of their time hiding in burrows and tunnels underground. They're among the rarest Pokemon available to catch in the wild, with an encounter rate around 1%, when they're not swarming.
- Radiata Stories: Tsuchinoko is a rare encounter in this game. It drops an item called "Tsuchinoko Dumpling," which fully recovers HP and VP.
- Forbidden Siren (Called just Siren in the US): Can be spotted a couple times in specific scenarios, one of which sees it squeezing into the drain of a bathtub.
- In Touhou canon, specifically Strange and Bright Nature Deity, Marisa adopted a rather cute tsuchinoko as a pet after chasing it out of a fairy's house.
- Yo Kai Watch: One of the franchise's Ensemble Darkhorses is a literal Tsuchinoko, named "Noko" in the English version. There's also a variant called Tsuchinoko Panda (named "Pandanoko" in English), who has a panda's black and white coloration.