When a character sees horrifying or unnatural things, they are Shocked and risk going insane. Character sanity is tracked using Shock Value.
Whenever the DM determines that something is suitable freaky, you must roll equal to or less than your Intellect. Success means you have remained strong in the face of the weird or terrible. Failure means you have cracked, just slightly, and will never be the same truly…you gain a point of Shock. These are permanent and stack and are only very rarely able to be removed.
When your Shock Value equals your Wisdom Score you suffer a permanent -1 penalty to hit, to damage, to saving throws, and to new HP gained at each level.
When your Shock Value exceeds your Wisdom Score, the first time and every time, the DM rolls on the Shock table and your character suffers a minor personality flaw or, eventually, a major madness. Everything you end up with can always get worse the more Shock checks you fail.
It takes a good long while before the Shock effects can be reduced or removed, and removing an effect never reduces your actual Shock Value. You may attempt to roll equal to your Charisma Score or lower to act normal for a turn, but you must do this every turn or every time your trigger comes into play.
When your Shock Value reaches 21, your character is so bucket-shitting crazy that they become an NPC.