Swamp Thing died two or three horrible deaths, and also gets abused by the forces of darkness regularly. I don't think he has any scars since plants are not like people, though.

Cyborg lost most of his body in an accident. I think that counts as a pretty big scar.

Poirot, OTOH, seems to have gone most of his career without sustaining any major injuries. Health problems, yes. Injuries and scars, no.