Old Stove cook up a thick, fuzz-coated brand of stoner rock powered by the guitar and vocals of Gabriel Freitas, with Lucas Braga on bass and Murilo Costa on drums locking in a heavy, desert-scorched groove. Their 2015 debut album #1 opened with the slow-burning "Place Pigalle" and showcased a band clearly schooled in the low-slung psychedelia of the genre's American forebears.

Old Throne is the one-man black metal vehicle of Fernando Count Old, a project he has driven since 2007 through a series of demos, EPs, and full-lengths steeped in anti-religious contempt and raw, uncompromising misanthropy. The 2013 album O Novo Mundo Pagão stands as a centrepiece of his catalogue, released through both the Japanese label Weird Truth Productions and domestic outlets.

Older Jack are a heavy metal and hard rock band from the German-heritage city of Pomerode in Santa Catarina, whose album Metal Uber Alles — a tongue-in-cheek nod to the genre's grand traditions — arrived as a limited CDr release. Their sound sits squarely in the classic heavy metal tradition, drawing on the melodic riff-driven energy that defined the genre in its formative decades.

Oldlands is a one-man black metal project helmed entirely by Vox Morbidus, drawing deeply on the raw, stripped-down aesthetics of 1980s and 1990s European black metal. After releasing the full-length Source of Eternal Darkness in 2019, the project matured with Oldmaster in 2023, a record structured like a vinyl side A/B split that pairs guttural and high-pitched vocals with keyboards and acoustic passages.

Omens of Plague is a Buenos Aires metalcore/melodic death metal band formed in 2009, featuring vocalist Gonzalo Roland, guitarists Francisco Cañardo and Nahuel Hadouken, bassist Rodrigo Ferreiro, and drummer Pazuzu Imdugud. The band released their debut full-length The Merciless Beyond on May 10, 2017, a 12-track record that drew praise for its technical guitar work and melodic death metal songwriting.

Omni Gear emerged in 2016 from the ashes of Rebel Machine, a heavy metal act the same members had been running since 2005, bringing a harder power metal focus to the new project. Their lyrical universe runs through science fiction, political commentary, and social themes, and the band placed the track "Fever Dream" on the Natal Metal Compilation III released through Dio Records.

Omniscience play an expansive, keyboard-laced atmospheric black metal anchored by multi-layered guitar work and the dual vocal interplay of Kalash and Archon. Their 2021 album Ancient Spell, released through Careless Records, draws its lyrical imagery directly from Magic: The Gathering lore, with tracks like "The Coming of Iona" and "Gates of the Mindless Temple" treating the game's mythology as genuine mythological source material.

One of Them is a Porto Alegre thrash metal outfit whose 2019 album Blind Faith, recorded at Hurricane Studio with producer Sebastian Carsin, brought together vocalist GG Mussi, guitarists Jeff Witt and Ivan Santos, bassist Alexandre Guterres, and drummer Jonas Koehler. The record marked a new phase for the band, arriving roughly a decade after their debut EP I Am One of Them and featuring a Portuguese-language track for the first time.

One Third of the Angels is a black metal duo formed by Ricardo Echeverria, also known from One Cross, and Wagner Santos, who plays in Nox Caelum and Revogar. The project surfaced in 2023 with the single "My Darkest Memory," channeling a cold, atmospheric approach rooted in the South Brazilian underground scene both members have long inhabited.