Sion is exceedingly difficult to kill – his mastery over his own body (as imperfect as it is), has given him tremendous vitality, and the near-constant agony he endures allows him to ignore attacks and wounds that would cripple or kill a normal human being... or even a Jedi.
Like most of the Sith Lords, Sion has few redeeming qualities. He is a cold, vicious killer driven only by the need to inflict pain and suffering on others – as the leader of a sect of Sith assassins sent to wipe out the Jedi Order, Sion and the player are destined to cross paths.