You create a phantasmal image of the most fearsome creature imaginable to the subject simply by forming the fears of the subject’s subconscious mind into something that its conscious mind can visualize: this most horrible beast. Only the spell’s Foe can see the Phantasmal Killer. You see only a vague shape. The target first gets a Will save to recognize the image as unreal to disbelieve the spell and suffer no ill effects. If that save fails, the phantasm touches the subject, and the subject must succeed on a Fortitude save or die from fear. Even if the Fortitude save is successful, the subject takes 1d3+1 points of bane damage per caster level.
Phantasmal Killer is a death effect and a fear effect, and as such, either Deathblock, Death Ward or any sort of fear immunity will provide immunity from this spell.