Sometimes people encounter an act of violence, or entity that floors them. Something truly horrific, weird, or strange. So seeing an angry savage dog wouldn't require it. But seeing an angry savage dog foaming at the mouth, the fur on its head slicked back by blood and gore, yes. Seeing someone shot, no. Finding a pile of corpses that have been machine gunned, yes. A group of people walking at night, no. Encountering the "Night Marchers", yes. Reading about Kahōʻāliʻi, no. Encountering Kahōʻāliʻi, yes.
When making a check the character must roll over an 10 (11 or better). The roll receives a bonus from willpower. Some creatures or situations have a bonus that is added to the target number. If the roll is successful, they have pulled themselves together and operate normally. If they fail they must run away or stand frozen in horror. They also temporarily lose 1 willpower point till they have slept. Characters regenerate one point of temporarily loss will every time they sleep. So if they lose more than one in a day it takes days to regain them. Now if they a roll a 1 it is an automatic failure. In addition to the effects of a normal failure they also permanently lose one point of willpower, and gain a mental disorder.
Roll 1d6 and consult the table
Psychosis or Psychotic break
The character suffers from abnormal social behavior and failure to recognize what is real. Common symptoms include false beliefs, unclear or confused thinking, visual and auditory hallucinations, reduced social engagement and emotional expression, and lack of motivation. Before attempting any task character must roll over a 10 (Wil bonus applies). If they fail they are distracted visual and audial hallucinations. Making giving any task a modifier of -6. Characters can be institutionalized to help remedy themselves of the psychosis. If they can Willpower roll of 15 or better they are cured. Institutionalization successful of not lasts, 1d12 months. If faced with another horror check, and they fail. They automatically slip back into psychosis again.
Phobia is an irrational fear of x. The phobia gained should have something to do with the experience that traumatizes the character. If attacked by a demon possessed dog, one should not gain a fear of flying for example. Character is at -5 for all rolls when dealing with this phobia.
Anxiety is a grouping of stress related disorders. Such as panic attacks, and OCD. Roll randomly or pick one. 1-2 panic attack, 3-4 OCD
Character when in a stressful situation must make a Willpower roll or be frozen in place unable to do anything, or runs away as best they can. (50/50 chance of either.)
Character develops 1d3 compulsive habits. If these habits are not followed to the letter, the character is distracted and irritated. -3 to all rolls.