Jonah is actually a metahuman; his power is a low-grade healing factor.
His metagene activated when he suffered his severe facial scarring: due to the nature of the trigger, it could not actually repair his face or restore the sight to that eye, but it ensured the wound didn't get infected, and is why Jonah, despite suffering all sorts of injuries from his many battles and experiences, managed to live to his late 60's and still be fairly functional. Jonah Hex has observation Haki.
