Inquisicion is a heavy metal institution from Santiago, Chile, founded in 1993 by guitarist Manolo Schäfler alongside drummer Carlos Hernández, operating briefly as Santa Inquisición before shortening their name in 1995. Their 1996 debut Steel Vengeance was the first Chilean heavy metal full-length in nearly a decade and earned them the Breakthrough Band of 1996 award; the band has since released six studio albums, including the conceptual Codex Gigas (2014, Australis Records) — nominated for best Chilean metal album at the 2015 Pulsar SCD awards — and Preacher and Lust (2016), with the lineup having shared stages with Mercyful Fate, Judas Priest, and Blind Guardian over their three-decade career.

Inraza is a groove metal and metalcore band from São Paulo, Brazil, founded in 2018 by veterans of the city's underground scene, with a lineup including vocalist Stephany Nusch and guitarist Gabriel Colonna. Drawing on influences such as Lamb of God, Fear Factory, and Sepultura, the band blends contemporary heaviness with melodic passages and socially engaged lyrics. Their debut album Infection was released in November 2020, followed by further studio work including (Still) Stuck and Sociexit.

Insane Devotion is a symphonic black metal band from Curitiba, Paraná, Brazil, active since 2000 and one of the more enduring acts from the city's extreme metal scene. Their discography spans multiple decades, opening with the split release In Inferioribus Terrae alongside Scorner in 2000, and continuing through Slaves Will Serve (2005), Infidel (2015), and Tormento (2022), the latter released via Mindscrape Music.

Insane Madness is a grindcore band from Natal, Rio Grande do Norte, Brazil, operating in the deathgrind and crustcore spectrum. The band released the EP Pandemia in July 2024, establishing themselves as a new entry in northeastern Brazil's growing extreme metal underground.

Insanecide was a heavy metal and hard rock trio from Volta Redonda, Rio de Janeiro, Brazil, active from 2013 until their split-up. The band combined the rhythmic weight of groove metal with melodic hard rock sensibilities, drawing comparisons to Pantera, and released the four-track EP Counter alongside a music video for the track "The Rift."

Insanitears is a doom/black metal band from Teresina, Piauí, Brazil, active since around 2019. The band explores themes of death, judgment, witchcraft, and the occult within a dark, slow-burning sound rooted in the Brazilian underground metal scene.

Insanity was a death/thrash metal band from Fortaleza, Ceará, Brazil, formed in 1989 under the name HON (Hexistence of Noise) by bassist/vocalist George Frizzo and guitarist Alberto Lopes before adopting the Insanity name later that year. The band released the demo "In Search of Reason" in 1990, recorded at Proaudio Studios in Fortaleza, and later issued the full-length "Phobia" in 1993 through Muvuca Records before splitting up in 2003.

Insanity Seas is a doom/death/sludge metal project from Porto Alegre, Rio Grande do Sul, Brazil, conceived by Henrique and Love Streit and active since 2021. Drawing lyrical inspiration from the cosmic horror fiction of H.P. Lovecraft, the band channels oppressive, slow-grinding riffs into an atmosphere of dread rooted in Lovecraftian mythology.

Insanity Storm is a melodic black metal band from Concepción, Chile, founded in 2023 by Countess Elizafer (Nicole Molina), who recorded all instruments and vocals for the debut album Caos Destrucción, released in December 2023. The band expanded to a full lineup with drummer Count Salvatore (Esteban Medina) and released the eight-track EP Eternal Winter in February 2025, with a conceptual narrative centered on the character Lilith; their upcoming album Winterworn is set for release through Solistitium Records of Germany, the former home of Behemoth, Tsjuder, and Horna.