To commemorate cold and flu season, we offer you The Book of Plagues, an efficient, flexible way for making your player characters sick. It's designed for compatibility with Dungeons & Dragons (5th Edition and 2024) and Pathfinder (both 1E and 2E), but it can probably be adapted to any d20-based RPG system with some conceptual mapping and simple math.

The Book of Plagues features 30 or so IRL diseases, ranging from the potentially lethal (bubonic plague) to the merely irritating (swimmer's itch), with the chance of contracting it, circumstances under which you might contract it, incubation period and symptoms expressed in terms compatible with D&D 5E and 2024 as well as both editions of Pathfinder.

Why would you want to introduce diseases into your fantasy RPG campaign? Well, maybe your players are getting a little too high on the hog and you want to force them to spend some resources, like a spell slot committed to cure disease or gold for a cure from the local temple. Maybe they've been dawdling and you want to use the risk of influenza or cholera to urge them to leave an encampment or a comfortable urban dwelling. Maybe you just want to add a touch of grim realism to what is, after all, a pre-modern world. Diseases with a creature vector, like malaria or Lyme Disease, can add a dangerous bit of potency to certain encounters.

Exactly when and how to use the system presented in this book is entirely up to you. Decide when it makes sense to force your players to check if their characters contract a certain disease — or just do so whenever you feel like it. If you can't decide on a disease to which to expose them, use the random affliction tables in the appendix, depending on whether you want a disease that is creature-borne, contracted from contaminated food or water, or spread through personal or environmental contact. When you're party is getting too smug, make 'em sick.