Normal mental balance is endangered when characters confront horrors, entities, or activities that are shocking, unnatural, and bewildering.Such encounters cause a character to lose points from his Sanity score, which in turn risks temporary, indefinite, or permanent insanity.If you adopt this variant in your campaign, the largest change will most likely be one of tone (this applies to an even greater extent if you adopt the entire Cthulhu Mythos that the variant is based on).As in the Call of Cthulhu Roleplaying Game, characters feel more vulnerable, for no matter how powerful they become, the dark gods are always greater.And yet, with such dark challenges come the opportunities for greater heroism.Sanity is the natural mental state of ordinary life.
In campaigns using these rules, characters gain a new attribute called Sanity.
This gradual descent is balanced in part by the powers that characters gain each time they overcome a horrific foe or grow in skill and expertise, but even as those characters grow in power, they know or fear that an even greater peril lies ahead—the threat of becoming permanently insane.
Because it affects the way that characters interact with the creatures and objects that they encounter on their adventures in many different and profound ways, this variant, perhaps more than any other in Unearthed Arcana, can alter the entire feel of a campaign.
Mental stability and lost Sanity points can be restored, up to a point, but psychological scars may remain.
Religion is not only a source of comfort or succor, but also a dangerous enemy.