Stick Figures
Stick figures, circle heads, and countryhuman-esk characters.
Immortals are, well, immortal. Most of them live in a plane between life and death, unseen and unheard by mortals, but capable of interacting with the mortal realm. The only way to achieve this state is to be cursed, or have a curse backfire upon one. Few have found a way to escape the plane, those who have are capable of hopping between the two planes, and keep their immortality.
Immortals are rare, with newer ones being hundreds of years old.