You'll Catch Your Death

I've previously outed myself as a recovering microbiologist, so it comes as little surprise that I liberally sprinkle disease and other such biological ephemera in my scenarios. (One of the players in my Los Angeles-set Unknown Armies game was bitten by an extradimensional raccoon, and was dismayed that her character became feverish and the bite wound became swollen despite passing her Fitness roll. I reminded her that fever is the sign that your body is doing what it's supposed to; the symptoms would have been far worse — and rules-influencing rather than merely descriptive flavor — had she failed.)

The following content originates from an early draft of No Rest for the Wicked. I'm glad to have dropped the prospect of cold weather as an antagonist, but the rules are still potentially useful, so here you are. As written, this is for Lamentations of the Flame Princess, but easily adaptable to any sort of old-school adventure game.

Hypothermia and Pneumonia

If player characters insist on sleeping outdoors on a cold, rainy night, they can potentially deal with the following complications:

If the player characters lack bedrolls and tents, the cold and wet threatens them with hypothermia. The player characters must save versus Paralyzation every turn or else lose a point of Constitution. Constitution lost to hypothermia potentially returns at a rate of 1 point per turn of rest, provided the characters are resting in a warm, dry space. Characters gain a +2 to the save if they have winter clothes.

If the player characters lack tents and winter clothing, sleeping in the cold, wet night threatens them with a respiratory ailment like bronchitis or pneumonia. If player characters spend more than 2 + Con modifier hours (minimum of 1 hour) out in the bad weather, the Referee should save versus Poison on their behalf. Failure indicates characters become feverish and are wracked with coughing fits within the next day or two. Three days after initial infection, the Referee should save versus Poison on the character's behalf again. (This roll is made at a -2 if the character is not resting during the infection, i.e. still adventuring.) Failure means the character loses 1 point of Constitution and 1d2 hit points. This saving throw repeats every 6 hours for 7 days. If the character survives the week, the disease passes. Lost Constitution returns at a rate of 1 point for every day of rest. At the Referee's option, a character might permanently lose 1 point of Constitution if their Constitution becomes low enough (maybe within Con 1-3).