You become harder to kill when possessed by the undead.

Prerequisite(s): Spell Focus (necromancy).

Benefit(s): Whenever you are possessed by an undead creature that you do not directly control, you gain a +4 bonus on saving throws against death effects. You don’t fall unconscious at negative hit points, and if you or the undead possessing you is forced to attempt a saving throw to resist ending the possession effect, you or your possessor gains a +4 bonus on the saving throw.