Mythological Cold Towers deal in slow, heavy doom that draws equally from the death-doom tradition and epic doom's grandiose sweep, with lyrical themes orbiting ancient South American civilizations, mythology, and lost monuments. Albums like Immemorial (2011) and Monvmenta Antiqva (2015) display the band's ability to balance crushing heaviness with melodic keyboard passages and an almost archaeological sense of atmosphere.

Mábura is an instrumental psychedelic stoner/doom metal trio from Rio de Janeiro, Brazil, formed in 2019, known for fuzz-heavy riffs and ritualistic atmospheres. The band released the EP "Heni" in August 2020 and contributed the track "Bong of God" to the compilation "Doomed & Stoned: The Instrumentalists" (2021); they later collaborated with Lagarto Rei on the two-song instrumental EP "Abyssopelagic."

Mães Morrendo is a doom metal project from São Paulo, Brazil, founded in 2019 as a solo endeavour by multi-instrumentalist Melissa Ângela, who also performs with Dirty Grave and the psychedelic doom band Melissa. The project blends doom metal with sludge, grunge, and rap influences, building a catalogue that includes releases such as "Corrosivo", "Hemorragia Social", and "Água-viva". By 2024 the project had expanded into a full power-trio lineup with Neli on drums and Bárbara Guieiro on bass.

Mërgim is a Buenos Aires sludge/post-metal trio consisting of Gustavo Cirigliano on guitar, Sebastián Manino on bass, and Nicolás Melichar on drums. They released their debut album Shpirti in March 2020, recorded at Estudio Instituto TAMABA, followed by the five-track record I in July 2022, produced with Martín Gandulfo at Estudio Paraíso.

Mórbida Exhumación is a death metal band from Ushuaia, Tierra del Fuego — one of the southernmost active metal acts in the world. The band released the EP Liberando el Dolor in 2020, followed by the full-length Alteracion Morbosa de la Personalidad in October 2021, a ten-track record with lyrics drawing on horror and gore themes.

Mörbidez is a one-man black thrash project that recorded its entire debut, Sob o Signo de Belial, between April and May 2020 at the creator's own Casa da Bruxa studio in Vitória. The album channels the ragged energy of first-wave black metal and South American speed metal through nine Portuguese-language tracks steeped in satanic imagery, and was released in June 2020 alongside a bonus covers EP titled Limbo.

Mörmo is a stoner/doom metal trio from La Plata, Argentina, formed in 2018, consisting of Gonzalo Soria on guitar, vocals, and synthesizers, Nicolas Reggiardo on bass and synthesizers, and Rodrigo Carlos on drums. The band released their debut demo Siluetas in August 2018, and followed it with the full-length Nueva razón in February 2023, recorded at Estudios Mirifico in La Plata and mastered by Gonzalo Villagra at Estudios Audion.

Mötim is a speed metal trio from Rio Grande do Norte comprising vocalist and guitarist Alexandre Almada, drummer Glenio, and bassist Gustavo. The band delivers fast, stripped-down heavy metal with an aggressive underground ethos, documented across a run of self-released recordings on Bandcamp including "Heavy Metal and Rotten Hearts" and "Genocida".

Mørk Visdom crafts raw symphonic black metal steeped in Luciferianism and occult darkness, releasing their debut "Fenrisulfr" through Impaled Records in 2012. The project has remained prolific, with subsequent releases including "Impure Nights of Dense Witchcraft" (2020) and "Obscure Symphonies (The Cursed Chant Of The Fallen Angels)" (2021) cementing their place in the extreme underground.