Illithids (mind flayers) in the Dungeons & Dragons setting are terrified of ghosts and undead beings in general, and for good reason. Undead are immune to psionic powers (even intelligent ones) and even undead who have brains can't be hurt by an illithid's extraction ability. This makes an illithid virtually powerless against such creatures, one of the few types of monsters they fear.
Hunter: The Vigil: Slashers may be very adept at killing people, but often find themselves ill-equipped to deal with vengeful ghosts. This makes Sin-Eaters particularly terrifying to slashers, because Sin-Eaters have powers that not only make them very hard to put down, but also allow the slasher's victims to rise from their graves and get revenge en masse.
Miscellaneous
Beast: The Primordial: This is one of the Anathemas a Hero can place upon the titular Beasts. A Beast under the Phobia Anathema develops a crippling fear of something semi-random (It tends to reflect the Beast's nature, but is never so common as to completely cripple the Beast's human or monstrous lives).
The Fear passion in Unknown Armies is that thing that sends you into full blown panic mode, and it is tied to one of the five Stresses. Someone with a fear of dogs, for example, may have been attacked by one, making it a Violence-related fear. Someone who fears fire, for another example, may have had their home burn down and everything in it destroyed, with nothing they could do to stop it, making it a Helplessness-related fear. When someone gets smacked with these fears, they have to make a stress check versus the appropriate stress, and failing them leads them down the road to madness.
