which of the lighting setttings for the legendary and mythic map packs make the best lighting for a scary feeling while on the map.
Gloomy, most likely. You can add some more for an increased feel. Pencil & Ink is also fairly well, mainly because it's a whole lot harder to see the map and your enemies, really. But I'd go with Gloomy.
Gloomy, juicy, old timey make a nice bloodred looking map with all the brown Sandbox has. Kill balls and red lights add to the effect.
If you wanted it to be really spooky, look for a canvas map with the Guardians blocked off. Then build the map in the dark part, maybe with the blue and red lights adding a little light?