Surprisingly this hasn't been easy to find. There are traditional songs like "La Bruja" and "La Llorona" that have been performed by numerous artists and there are a number of other traditional songs with fairly minor key chord progressions like "La Petrona." (Some of the moodier renditions I've come across are Mamselle Ruiz's and Lila Downs', but neither artist is strictly "dark.") Still, I haven't really found anyone who is consistently gloomy all around. When I search for "dark Mexican folk" I either get results for either Mexican goth bands (that sound like Euro style goth bands) or just Mexican folk without the "dark" part (or it thinks I'm referring to Afro-Mexican music). I'm imagining something more like the Mexican equivalent of "dark Americana" like Tarantella, 16 Horsepower, DBUK, Munly, etc. that draws on Mexican traditions and instruments, even if it also incorporates rock or whatever other influences. Does such a thing exist?