Looking Upon the Face of a Dead God: the aftermath of a 1D10/1D100 SAN test

art from Lovecraft: The Blasphemously Large First Issue by Daniel Govar and Mat Lopes

In Delta Green, if a Great Old One makes a big enough appearance in the game for you to have to make a SAN roll, the game's usually over. But sometimes it's not the end. Maybe a Shan only briefly exposed your mind to Azathoth as a punishment, or like Johansen, you ram Cthulhu in the face with a steamboat, who understandably decides to go back to sleep. You've still lost 1D10, 1D20, or 1D100 SAN, which is an awful lot. Just because Yog-Sothoth didn't let the Old Ones break through and trample all over the earth doesn't mean you survived. There's a good chance you're babbling at 0 SAN or some other number low enough for an exit from field work. In this post, I'm going to crunch the numbers to find the probabilities of the different results of a 1D10/1D100 or 1D20/1D100 SAN test.

An Analysis of SAN Loss in Delta Green

When Agents (and theoretically NPCs) encounter unnatural beings, they usually have to make a SAN test and risk losing some SAN. Most SAN losses in Delta Green follow a rule of thumb set out in the Agent's Handbook's Sanity chapter.

If the cost of failing a SAN test is 1D6 or less, the cost of success is usually zero. If the cost of failure is 1D8 or 1D10, the cost of success is usually 1. Some unnatural events and encounters are even more catastrophic (AH, 66).

You can map out the progression of SAN loss like so: 0, 0/1, 0/1D4, 0/1D6, 1/1D8, 1/1D10, 1D4/1D12, 1D6/1D20, and 1D10/1D100. We don't find 1D10/1D100 until we open the Handler's guide, and 1D4/1D12 is purely a theoretical SAN loss that fits very nicely between 1/1D10 and 1D6/1D20 but I've never seen it in any published DG material. 

EDIT: as of Fall 2021, we actually now have an official 1D4/1D12 SAN loss in ARCHINT.

Some listed SAN losses deviate from this progression. Most of these anomalies are unnatural, but first I'll cover the mundane anomalies found in the Agent's Handbook.