The luz mala
The luz mala, or evil light, is a bright ball of light reported floating just above the ground in rural Argentina and Uruguay. Country people have long taken it for a soul in torment.
Wikipedia says that in Argentina and Uruguay, will-o'-the-wisp lights go by the name luz mala, meaning evil light. It ranks high among the myths of both countries' folklore. People fear it, and it is seen mostly in the countryside. It is described as a very bright ball of light hovering a few inches off the ground.
Juan B. Ambrosetti recorded the rural explanation in 1917. The people he spoke to said the light comes from a soul suffering for some reason, and that if they pray for it, the light will not follow them. Being followed was what they feared.
A 2013 travel feature in Uruguay's El País says the light is commonly taken for a soul in torment, the spirit of someone who never received a Christian burial. The advice on meeting one was to say a prayer and then bite the sheath of your knife. As a last resort you faced it with a blade, since guns were said to be useless against it. The article also names Ailen mulelo, which it glosses as a burning ember that walks, and gives Boy Tata as another name for it.
"Según ellos, la luz mala procede de un alma que se halla en pena por cualquier motivo, y dicen que rezando por ella la luz no los sigue, que es a lo que tienen miedo."
- La Luz Mala y otros fuegos horripilantes, El País (Uruguay), Viajes (2013)
- Will-o'-the-wisp, Wikipedia