Acrostic are a thrash metal band from Viña del Mar who describe their sound as "Noisethrash" — a blend of old-school thrash, hardcore punk, and crust rooted in the Bay Area and European thrash traditions. The trio of Janito Attack, Pablito Attack, and Pelao Attack released their full-length "Sincretismo-Posguerra" in November 2016 on Underground Defenders Records, a 11-track record recorded at JRP Studios in Viña del Mar and limited to 500 copies.

Acrópole is a black metal band from Rio Brilhante and Dourados in Mato Grosso do Sul, active since 2020. Based deep in Brazil's interior rather than in the traditional urban metal centers, the band operates in the raw, atmospheric tradition of Brazilian black metal, contributing to what is a notably sparse but growing extreme metal presence in the Mato Grosso do Sul state.

Acsa is a heavy metal band from Cipolletti, in the Patagonian province of Río Negro, Argentina, formed under their current name around 2014 after originating as Pucara in 2009. The band's lineup of Javier Burgos on vocals, David Ariel Rodríguez on guitar, Damián Zeballos on bass, and Alejandro Rodríguez on drums recorded their debut album "Sangriento Final" at Horus Estudio in Cipolletti in 2021. Their sound draws from the classic Argentine heavy metal tradition while aiming for a heavier, more original direction.

Act of Revenge is a groove/death metal and deathcore band from Salvador, Bahia, formed in 2015 and anchored by vocalist Danfacto Oliveira, whose performance earned the band Best Vocalist honors at the Prêmio Palco do Rock 2014 popular vote — the same year they also won Best Band. Their 2018 EP 5 Atos delivers heavy, groove-driven material entirely in Portuguese, and the band has performed across multiple editions of the Festival Palco do Rock, establishing them as one of Salvador's most visible acts in the heavy underground.

Actum Est is a symphonic black metal band from Belo Horizonte, Minas Gerais, featuring a six-piece lineup that incorporates cello alongside traditional metal instrumentation — a rare texture in Brazil's black metal scene. Formed in 2005 (catalogued under their current activity since 2013), the band released the demo Obscure Symphonies Into the Black Mantle in 2006, channeling themes of occultism and darkness through a lush, orchestrated approach that sets them apart from the rawer strains of the Brazilian underground.

Ad Baculum is a black metal project from Salvador, Bahia, led by Lord Hades — formerly the vocalist of legendary Brazilian cult act Mystifier — who handles all instruments except drums. The band's debut Blackness Doctrine (2011) drew directly from the raw black/death vein Hades helped pioneer in Mystifier, while the third album Opening the Abyss (2016), released on Brazilian Ritual Records, shifted toward slower, doom-saturated tempos with howling, cavernous vocals and cover art taken from Gustave Doré's illustrations of Dante's Inferno.

Ad Extremum is a black metal band from Brasília, Brazil, formed in 2013 and signed to Nox Bellum Prod. Their music explores themes of Satanism, occultism, and suicide, rooted in the raw, atmospheric tradition of Brazilian black metal.

Ad Inferi is a symphonic metal band from São Paulo, Brazil, formed in 2020 from the ashes of the symphonic outfit Sacra. The group features vocalist Alessandra Lodoli alongside guitarist Lucas Moretto, and released their debut album "The Immaculate" with the single "The Red Lake" as an early showcase of their orchestral, dramatic sound.

Ad Inferno is a Brazilian black metal project that emerged in 2022, featuring members drawn from Campo Grande, Curitiba, and Rio de Janeiro. Their debut full-length "A Senda do Abismo (Spiritus Pestilens)", recorded and released in late 2022, presents a cold, underground black metal aesthetic.