"Downfall" is not an adjective, nor is it a noun for a type of person. Definition of downfall
You can say that a person has "fallen down" of course, when they fall on the floor, or fall down the stairs.
You can say that someone is "downtrodden", meaning that someone else has treated them as an inferior, sometimes leading to the downtrodden person actually feeling inferior. A very domineering husband might have a downtrodden wife.