Ever heard of the Nicaraguan/Costa Rican Cegua? It’s a woman who seduces men (travelers , but most often exposing womanizers and drunkards) but when they are near her and excited she transforms into her true nature which has the head of a rotting horse (in El Salvadoran folklore she just becomes a hag known as Ciguanaba/Ciguanahual). The name has a root in the Nahuat word for woman “cihuet” and this spirit (according to lore) drives men literally insane, causes them to get lost/disoriented, catch a fever and/or die.