The idea of adversity rolls starts in an easy-to-overlook section on attributes in Men & Magic:
Constitution 13 or 14: Will withstand adversity
Constitution of 9 - 12: 60% to 90% chance of surviving
Constitution 8 or 7: 40% to 50% chance of survival
No real explanation, although an earlier comment about "how well the character can withstand being paralyzed, turned to stone, etc." suggests that this is the early version of the system shock roll, or a Constitution check. What I decided to do was to use this, or something like it, to resist or recover from critical injuries and disease.
- Damage > Constitution = Critical Injury
- 3d6 > Constitution = Catch Disease (after exposure)
- 3d6 <= Constitution = Critical Injury or Disease Healed
It's typically a 3d6 roll, but Minor Diseases (Cough, Sneeze, Sniffles) only use 2d6, and some serious stuff requires 4d6 or more. It's a very tiny disease system, compared even to the simple suggestion I posted ages ago: no disease levels, not much disease detail, just two broad types of disease:
Minor Diseases lower reaction rolls, reduce surprise chances, or have other nuisance symptoms that don't prevent adventuring. Roll every day to recover.
Major Diseases prevent the use of a body part or incapacitate. Roll every week to recover; if a vital organ is affected, a failed roll after the first week means death.
All of this so far is much longer than what I actually wrote in the article. But what I wanted to focus on here was the way you catch diseases. I don't see the point in having too much disease in the game, especially at the start. There's the obvious exposure to filth, and there's infection from not cleaning and bandaging wounds. All mostly avoidable. But I make a brief notation in the article that dungeon diseases have a level equal to half the dungeon level (if associated with a place) or half the monster's hit dice (if passed on by a monster's attack.) The obvious example is mummy rot, although that is specifically a magical disease, not curable by bed rest or mundane treatment (but Leeches can cure it.)
(In the article, I didn't mention whether to round up or round down. In truth, I was undecided. But I'm thinking now it should be "round up".)
The implications of this? Diseases on the 4th level of the dungeon would be 2nd level, with 2d6 adversity checks to resist or recover. In other words, these would be minor diseases, mere symptoms like an annoying cough that could spoil surprise, or a rash that could provoke negative reactions when bargaining with merchants. On the 1st and 2nd levels of the dungeon, there probably shouldn't be any diseases to worry about, not even ear seekers and rot grubs.
On the 5th level, that's where you could encounter major diseases, tainted waters that could put you away for a couple weeks or blind you. Or a 5 HD giant lizard could have an infectious bite that makes an arm or a leg useless until you recover.
Ear seekers and rot grubs are combo monster-and-disease. The revised ear seeker would be 3 dice monster that attacks the ear, success means it crawls inside, damage is ignored except to compare it to Constitution to see if the victim goes deaf in that ear. Every week, make an adversity roll to see if it reaches the brain, where it does damage and causes unconsciousness. A second failed adversity roll means death.
The revised rot grub is likewise 3 dice, attacks exposed flesh (or crrawls around looking for an opening,) and does damage; damage > Constitution means it burrows into the flesh and infects, followed by weekly adversity rolls to see if it reaches the heart. A second failed adversity roll again means death.
Both are still pretty serious, but there's plenty of warniing and time to address the situation. What I always hated about the official ear seeker and rot grub is that they had such byzantine rules and unusual cure restrictions, which add nothing.
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