Circadia is a heavy metal and hard rock band from Catriel, Río Negro, Argentina, drawing on classic 1980s and 1990s metal influences. The band has released recordings including the singles Leonidas and the EP Sucesos, building a following in the Patagonian underground metal scene.

Circle of Fear is a gothic metal band from San Antonio de Arredondo, Argentina, whose name is taken from a HIM song. The band released the single Deep Emotional Modus Operandi, a dark and atmospheric piece that drew coverage from international metal media in early 2026.

Circulo Negro is an independent black metal band from Itaituba, Pará, Brazil, formed around 2013–2014. The band explores themes of witchcraft and satanism and released the demo "Supremacia Herege" in 2015, distributed through Brazilian underground distros such as Jazigo Distro.

Cirrhosis is a death metal band from Uberlândia, Minas Gerais, Brazil, originally formed in 1988 by members who also played in Sarcófago; after dissolving in 1993 they reformed in 2001 and signed with the legendary Cogumelo Records. The band released the full-lengths "Alcoholic Death Noise" (2002) and "Drinks From Hell" (2009), built around a booze-and-brutality lyrical identity rooted in the classic Brazilian extreme metal tradition.

Clamatorius is a black/death metal band from Goiânia, Goiás, Brazil, originally active from 1999 to 2005 under their own name after an earlier incarnation as Postumus (1998–1999). The band is notable for fusing extreme metal with Christian lyrical themes and released the five-track album "Consummatum Est" through Blackened Label Records.

Clan dos Mortos Cicatriz is a death-punk band from Curitiba, Paraná, Brazil, blending raw black metal, death metal, and hardcore punk into what the underground has called "nekro-hardcore." The band released their debut album "Técnicas de Morte" in March 2025 via Sentient Ruin Laboratories, a 15-track, 25-minute record described as a grim manifesto drawing imagery from slums, prisons, morgues, and war zones.

Claustro is a groove metal band from Buenos Aires and Hurlingham, Argentina, formed in 2011 by guitarist and vocalist Cristian Karpluk alongside guitarist Mariano Valsecchi, bassist Dante Roncali, and drummer Juan Marcelo Hernández Herrero. The band has released three studio albums — Pulsión Animal (2015), H.I.S. (2017), and En el umbral de la extinción (2020) — building a catalog that blends groove and thrash metal with hard rock influences.

Claustrofobia is a death/thrash metal trio from Leme, São Paulo, Brazil, formed in 1993, and widely regarded as one of the most important underground extreme metal bands to emerge from Brazil. The band has toured extensively through South America, Europe, and the United States — sharing stages with Slayer, Iron Maiden, Sepultura, and Napalm Death — and has released a string of albums including "Fulminant" (2005), "I See Red" (2009), and "Unleeched" (2022).

Clava is a death/thrash metal and hardcore band from São Paulo, Brazil, formed in 2024. The band operates in the tradition of Brazilian extreme metal crossover and is listed as active on Metal Archives. As a very recently formed act, they have yet to accumulate significant press coverage beyond their initial registration.