In high-fantasy games characters encounter monsters and horrors and it is their every day basis. No walking dead, horrible monsters or weird spells make heroes blink their eyes before they attack trying to destroy the nasty.
Different thing is in Lamentations of the Flame Princess Weird Fantasy. In LotFP monsters and other things are rare. So rare that even rules don't stat them (only exception is Vampire what is an example monster). In LotFP weird and horror should be weird and horror.
Sometimes you need a little push from rules to simulate this. One of the most famous example would be Call of Cthulhu roleplaying game where insanity rules are most important in whole game. You see and experience horrible things, you go nuts.
Even though this article is mainly for LotFP you can use it with every retroclone or other d20 game and with minor tweaks adapt it to your favorite game system.
What Causes Dread?
1. Something unexplainable and horrific
2. Mutilated corpses, walking dead
3. Horrible, strange and unnatural incidents (it rains blood, swarm of flesh eating frogs ripping flesh from everyone in the village, moon has grinning devil face...)
4. Strange monsters
5. Monsters and beings beyond understanding or from other planes/dimensions
6. Reading something not meant for mortals (occult books with horrible secrets better not to know)
Level Of Dread
Depending how horrible the incident or vision is dread has it's level. Levels are 10, 15, 20, 25, 30 depending on how horrible the incident or vision is. Seeing a mutilated corpse would be level 10 when horrible monster from other dimension causing all the surroundings to look strange and different would be 30.
To Roll Against Dread
Roll d20 and add your Wisdom bonus against dread level. If you success your character is not affected by dread. If you fail the roll roll Effect Of Dread table and add the difference of dread level and your failed roll to the result.
Example: Dread level is 20 and d20 roll + Wisdom bonus score is 15. Add +5 to Effect Of Dread table roll.
Effect Of Dread Table
Roll d20 and add difference of failure score and dread level to the roll.
1-5: Scared. Loose 1 from every roll you do for the rest of the scene.
6-9: Horrified. Loose 5 from every roll you do for the rest of the scene.
10-14: Petrified. Loose 1d6 turns and after it loose 5 from every roll you make.*
15-17: Catatonic Loose 1d6 turns. After those turns roll save versus paralyze to regain mobility.*
18-20: Insanity. Catatonic and also roll insanity table.
*When petrified or catatonic only use armor for AC
Roll d6 to see effect of insanity.
1 - Mental scars. Loose 1 point of Wisdom permanently.
2 - Fobia. Take a related fobia. When situation could trigger your fobia suffer -5 to all rolls.
3 - Nightmares and angst. Roll save versus magic every morning in game time to prevent -2 to all rolls that day.
4 - Nuts. Come up with an insanity. Loose 2 permanently from Charisma and roleplay it (blabbering with yourself, obsessive-compulsive behavior etc.)
5 - Gain both Mental scars and Fobia.
6 - Insanity. Loose control of your character for 1d6 days. After it roll Insanity table again. Insane character can do basic things like defend himself but cannot think logically and is a burden to other party members.