The carbuncle is a creature described in Jorge Luis Borges's Book of Imaginary Beings. Allegedly sighted in 16th century South America, the carbuncle is described as a small animal with a jewel or small mirror on its forehead. Depictions vary between quadrupedal and bipedal, and is most often depicted as a mammal, though reptilian carbuncles are not uncommon. The gem in question is almost always red, often a ruby or garnet, since the name of the creature is derived from a word for red gemstones, which were once thought to have magical powers. That said, variants with other gem stones are not unheard of. Carbuncles are said to bring great wealth and fame, and in some works, the gem may be a source of magical power.
Although originally described as rodent-like and having shells, most modern works depict them resembling a cat, rabbit, fox, or a mix of the three. They often show up in fantasy media, but are particularly common in Eastern RPGs, especially Mons Series. Expect them to be an adorable mascot character. Occasionally they will be treated as a rare Metal Slime style of monster, alluding to the association with wealth. Note that a creature doesn't need to explicitly be called a carbuncle to be an example, as long as it still fits all the other criteria. The gem must be an organic part of the creature, animals wearing jeweled accessories on their head do not count.
- Cardcaptor Sakura: The Dash card takes the form of a fox/cat/rabbit hybrid with a blue jewel on its forehead. The Dash also makes an appearance in Tsubasa -RESERVoir CHRoNiCLE-.
- CLAMP: Mokona, the recurring mascot who first appeared in Magic Knight Rayearth, is depicted as a rabbit-like creature with a red gem on its forehead.
- Digimon Tamers: Calumon is a small Cartoon Creature with a red gem on its forehead, and its name is derived from "carbuncle". It is the source of digivolution in this series universe. Armadillomon from Digimon Adventure 02 may also be based on earlier armadillo-like carbuncles, as it has a red diamond-shaped marking on its forehead that is depicted as shining in some illustrations. Dorumon also has a large red jewel on its head, although it's larger than most examples and resembles a mammalian dinosaur.
- Tenchi Muyo! has the cabbit species, half-cat, half-rabbit with jewels on their foreheads. Most of them have red jewels, but Ken-Ohki has a yellow one.
- Yu-Gi-Oh!: The Crystal Beast Ruby Carbuncle card resembles a cat and features another larger gem on the tip of its tail in addition to the one on its forehead.
- In Medieval Europe, there was the toadstone. Toadstones were said to be jewels that reside in the heads of toads and protect them from their own poison. By extracting the toadstone, a human could protect against and cure themself from poison, and so they were often incorporated in (luxurious) jewelry. Earlier myths described similar stones as growing within the brains of dragons, which had a number of magical properties but only if extracted from the skull of a living beast — otherwise, they'd lose all luster and power. These days, it's known that toadstones are actually the fossilized teeth of Lepidotes, an extinct genus of fish.
- Book of Imaginary Beings is the Trope Maker. Like some other creatures in the book, Jorge Luis Borges made the carbuncle up more or less from whole cloth. The carbuncle is described as a small animal reported by conquistadors in South America. They were never seen clearly, so nobody actually knows if they are birds or mammals. They have small red stones or mirrors in their foreheads, similar to opals or to actual carbuncles, a name used for rubies or garnets, which are reputed to bring luck if obtained. Many hunted for the creature and its gem, but no-one succeeded. Borges further compares the carbuncle to the dragon and the toad, which were reputed to also bear precious stones in, respectively, their brains and their foreheads.
- Dungeons & Dragons: The Carbuncle is a recurring monster, and one of the earlier depictions in modern fantasy fiction. Unlike later cutesy catlike depictions common in Eastern works, this carbuncle is described as being armadillo-like.
- Pathfinder: Carbuncles are weakly magical, awkward-looking reptiles whose forehead "gems" are actually fingernail-like growths. Nonetheless, they're sometimes sought out as Familiars, usually by the Conspicuous Consumption-obsessed Kalistocrats or by those who appreciate their mild Telepathic powers.
- Elona: Carbuncles appear as catlike monsters with long ears and a red gem on their heads. Elona+ adds a higher level Ruby Carbuncle which is a purple recolor of the unrelated twintail monster. Strangely, a regular carbuncle can evolve into a manticore in Elona+.
- Final Fantasy: Carbuncles are a recurring summon. Their appearance varies wildly depending on the game, but usually resemble a fox or squirrel. In some games, their gem is horn-shaped.
- Pokémon: Espeon is partly based on the carbuncle, and partly based on the nekomata, being depicted as a cat with a split tail and a jewel on its forehead. Persian also has some elements, as it has a red gemstone on its head. There is also Carbink, where most of the creature's body is a gemstone. Diancie may also be based on the myth, although it's humanoid in shape.
- Puyo Puyo: Carbuncle is, as you can imagine from the name, a carbuncle and a Series Mascot alongside the titular Puyo. This depiction is yellow and resembles a rabbit, and his debut in Madou Monogatari 2 is one of the earlier examples of the cutesy, Japanese-style carbuncle.
- Puzzle & Dragons: Carbuncles are a common type of monster, coming in ruby, sapphire, emerald, amethyst, and topaz varieties. They are one of the Series Mascot monsters.
- Never Satisfied: Philomena's armadillo familiar Tully has an emerald on his forehead so his owner can use it to do magic.
- Subeta has the Kora, which resembles a cat or fox, has tentacles protruding from its ears and tail, and a diamond on its forehead. There is also the Mahar, which is more reptilian and has gems all over its body, in addition to the forehead.