SRD:Phantasmal Killer

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 subject can see the phantasmal killer. You see only a vague shape. The target first gets a Will save to recognize the image as unreal. 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 3d6 points of damage.

If the subject of a phantasmal killer attack succeeds in disbelieving and is wearing a helm of telepathy, the beast can be turned upon you. You must then disbelieve it or become subject to its deadly fear attack.