Curses left by Otòn, also called "Louzo's Curses" or other various names, using his personalized magic.
Shadows are an “enemy” created by Otòn; they are always a fully inky black with only slight features(eyes and teeth usually) in a distinguishable white, even when impersonating others. On their own, they do not really think or etc., because they don't have souls/hearts. They are more like masses of magic(aka they're curses!!) that responds to its surroundings... kinda similar to plants. They can only reflect the hearts of those around them, or do exactly what Oton wants them to do.
They were created with the intent of aiding mortals from undead when Erzulie was cursed for a period of time.
Oton's curses function only slightly different depending on the era;
Beginning
After Death
Current
Cotton