I’m not sure this song explicitly qualifies as a “Día de Los Muertos” entry, but it is my favorite Mexican folk song and there’s definitely a somber message and meaning to it. It plays off the prominent Mexican folklore figure La Llorona, a mother who loses her children and becomes a spirit that steals the children of others (if I remember correct). I believe each artist tweaks the lyrics slightly to fit their vision of La Llorona. A version of the song was featured in Coco, but I prefer this version sung by Angela Aguilar. Aguilar was born in Los Angeles, but it is widely recognized as a Mexican artist. This video was shot specifically for the holiday I believe.
La Llorona - Ángela Aguilar